11cb0ef41Sopenharmony_ci<!DOCTYPE html> 21cb0ef41Sopenharmony_ci<html lang="en"> 31cb0ef41Sopenharmony_ci<head> 41cb0ef41Sopenharmony_ci <meta charset="utf-8"> 51cb0ef41Sopenharmony_ci <meta name="viewport" content="width=device-width"> 61cb0ef41Sopenharmony_ci <meta name="nodejs.org:node-version" content="v18.20.1"> 71cb0ef41Sopenharmony_ci <title>V8 | Node.js v18.20.1 Documentation</title> 81cb0ef41Sopenharmony_ci <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback"> 91cb0ef41Sopenharmony_ci <link rel="stylesheet" href="assets/style.css"> 101cb0ef41Sopenharmony_ci <link rel="stylesheet" href="assets/hljs.css"> 111cb0ef41Sopenharmony_ci <link rel="canonical" href="https://nodejs.org/api/v8.html"> 121cb0ef41Sopenharmony_ci <script async defer src="assets/api.js" type="text/javascript"></script> 131cb0ef41Sopenharmony_ci <style>@media(max-width:574px){.with-44-chars>.js-flavor-selector{float:none;margin:0 0 1em auto;}}</style> 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<div class="header-container"> 991cb0ef41Sopenharmony_ci <h1>Node.js v18.20.1 documentation</h1> 1001cb0ef41Sopenharmony_ci <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> 1011cb0ef41Sopenharmony_ci <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> 1021cb0ef41Sopenharmony_ci <path fill="none" d="M0 0h24v24H0z" /> 1031cb0ef41Sopenharmony_ci <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/> 1041cb0ef41Sopenharmony_ci <path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/> 1051cb0ef41Sopenharmony_ci </svg> 1061cb0ef41Sopenharmony_ci <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> 1071cb0ef41Sopenharmony_ci <path d="M0 0h24v24H0z" fill="none" /> 1081cb0ef41Sopenharmony_ci <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 10.5H1v2h3v-2zm9-9.95h-2V3.5h2V.55zm7.45 3.91l-1.41-1.41-1.79 1.79 1.41 1.41 1.79-1.79zm-3.21 13.7l1.79 1.8 1.41-1.41-1.8-1.79-1.4 1.4zM20 10.5v2h3v-2h-3zm-8-5c-3.31 0-6 2.69-6 6s2.69 6 6 6 6-2.69 6-6-2.69-6-6-6zm-1 16.95h2V19.5h-2v2.95zm-7.45-3.91l1.41 1.41 1.79-1.8-1.41-1.41-1.79 1.8z"/> 1091cb0ef41Sopenharmony_ci </svg> 1101cb0ef41Sopenharmony_ci </button> 1111cb0ef41Sopenharmony_ci </div> 1121cb0ef41Sopenharmony_ci <div id="gtoc"> 1131cb0ef41Sopenharmony_ci <ul> 1141cb0ef41Sopenharmony_ci <li class="pinned-header">Node.js v18.20.1</li> 1151cb0ef41Sopenharmony_ci 1161cb0ef41Sopenharmony_ci <li class="picker-header"> 1171cb0ef41Sopenharmony_ci <a href="#"> 1181cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 1191cb0ef41Sopenharmony_ci Table of contents 1201cb0ef41Sopenharmony_ci </a> 1211cb0ef41Sopenharmony_ci 1221cb0ef41Sopenharmony_ci <div class="picker"><div class="toc"><ul> 1231cb0ef41Sopenharmony_ci<li><a href="#v8">V8</a> 1241cb0ef41Sopenharmony_ci<ul> 1251cb0ef41Sopenharmony_ci<li><a href="#v8cacheddataversiontag"><code>v8.cachedDataVersionTag()</code></a></li> 1261cb0ef41Sopenharmony_ci<li><a href="#v8getheapcodestatistics"><code>v8.getHeapCodeStatistics()</code></a></li> 1271cb0ef41Sopenharmony_ci<li><a href="#v8getheapsnapshot"><code>v8.getHeapSnapshot()</code></a></li> 1281cb0ef41Sopenharmony_ci<li><a href="#v8getheapspacestatistics"><code>v8.getHeapSpaceStatistics()</code></a></li> 1291cb0ef41Sopenharmony_ci<li><a href="#v8getheapstatistics"><code>v8.getHeapStatistics()</code></a></li> 1301cb0ef41Sopenharmony_ci<li><a href="#v8setflagsfromstringflags"><code>v8.setFlagsFromString(flags)</code></a></li> 1311cb0ef41Sopenharmony_ci<li><a href="#v8stopcoverage"><code>v8.stopCoverage()</code></a></li> 1321cb0ef41Sopenharmony_ci<li><a href="#v8takecoverage"><code>v8.takeCoverage()</code></a></li> 1331cb0ef41Sopenharmony_ci<li><a href="#v8writeheapsnapshotfilename"><code>v8.writeHeapSnapshot([filename])</code></a></li> 1341cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#v8setheapsnapshotnearheaplimitlimit"><code>v8.setHeapSnapshotNearHeapLimit(limit)</code></a></span></li> 1351cb0ef41Sopenharmony_ci<li><a href="#serialization-api">Serialization API</a> 1361cb0ef41Sopenharmony_ci<ul> 1371cb0ef41Sopenharmony_ci<li><a href="#v8serializevalue"><code>v8.serialize(value)</code></a></li> 1381cb0ef41Sopenharmony_ci<li><a href="#v8deserializebuffer"><code>v8.deserialize(buffer)</code></a></li> 1391cb0ef41Sopenharmony_ci<li><a href="#class-v8serializer">Class: <code>v8.Serializer</code></a> 1401cb0ef41Sopenharmony_ci<ul> 1411cb0ef41Sopenharmony_ci<li><a href="#new-serializer"><code>new Serializer()</code></a></li> 1421cb0ef41Sopenharmony_ci<li><a href="#serializerwriteheader"><code>serializer.writeHeader()</code></a></li> 1431cb0ef41Sopenharmony_ci<li><a href="#serializerwritevaluevalue"><code>serializer.writeValue(value)</code></a></li> 1441cb0ef41Sopenharmony_ci<li><a href="#serializerreleasebuffer"><code>serializer.releaseBuffer()</code></a></li> 1451cb0ef41Sopenharmony_ci<li><a href="#serializertransferarraybufferid-arraybuffer"><code>serializer.transferArrayBuffer(id, arrayBuffer)</code></a></li> 1461cb0ef41Sopenharmony_ci<li><a href="#serializerwriteuint32value"><code>serializer.writeUint32(value)</code></a></li> 1471cb0ef41Sopenharmony_ci<li><a href="#serializerwriteuint64hi-lo"><code>serializer.writeUint64(hi, lo)</code></a></li> 1481cb0ef41Sopenharmony_ci<li><a href="#serializerwritedoublevalue"><code>serializer.writeDouble(value)</code></a></li> 1491cb0ef41Sopenharmony_ci<li><a href="#serializerwriterawbytesbuffer"><code>serializer.writeRawBytes(buffer)</code></a></li> 1501cb0ef41Sopenharmony_ci<li><a href="#serializer_writehostobjectobject"><code>serializer._writeHostObject(object)</code></a></li> 1511cb0ef41Sopenharmony_ci<li><a href="#serializer_getdatacloneerrormessage"><code>serializer._getDataCloneError(message)</code></a></li> 1521cb0ef41Sopenharmony_ci<li><a href="#serializer_getsharedarraybufferidsharedarraybuffer"><code>serializer._getSharedArrayBufferId(sharedArrayBuffer)</code></a></li> 1531cb0ef41Sopenharmony_ci<li><a href="#serializer_settreatarraybufferviewsashostobjectsflag"><code>serializer._setTreatArrayBufferViewsAsHostObjects(flag)</code></a></li> 1541cb0ef41Sopenharmony_ci</ul> 1551cb0ef41Sopenharmony_ci</li> 1561cb0ef41Sopenharmony_ci<li><a href="#class-v8deserializer">Class: <code>v8.Deserializer</code></a> 1571cb0ef41Sopenharmony_ci<ul> 1581cb0ef41Sopenharmony_ci<li><a href="#new-deserializerbuffer"><code>new Deserializer(buffer)</code></a></li> 1591cb0ef41Sopenharmony_ci<li><a href="#deserializerreadheader"><code>deserializer.readHeader()</code></a></li> 1601cb0ef41Sopenharmony_ci<li><a href="#deserializerreadvalue"><code>deserializer.readValue()</code></a></li> 1611cb0ef41Sopenharmony_ci<li><a href="#deserializertransferarraybufferid-arraybuffer"><code>deserializer.transferArrayBuffer(id, arrayBuffer)</code></a></li> 1621cb0ef41Sopenharmony_ci<li><a href="#deserializergetwireformatversion"><code>deserializer.getWireFormatVersion()</code></a></li> 1631cb0ef41Sopenharmony_ci<li><a href="#deserializerreaduint32"><code>deserializer.readUint32()</code></a></li> 1641cb0ef41Sopenharmony_ci<li><a href="#deserializerreaduint64"><code>deserializer.readUint64()</code></a></li> 1651cb0ef41Sopenharmony_ci<li><a href="#deserializerreaddouble"><code>deserializer.readDouble()</code></a></li> 1661cb0ef41Sopenharmony_ci<li><a href="#deserializerreadrawbyteslength"><code>deserializer.readRawBytes(length)</code></a></li> 1671cb0ef41Sopenharmony_ci<li><a href="#deserializer_readhostobject"><code>deserializer._readHostObject()</code></a></li> 1681cb0ef41Sopenharmony_ci</ul> 1691cb0ef41Sopenharmony_ci</li> 1701cb0ef41Sopenharmony_ci<li><a href="#class-v8defaultserializer">Class: <code>v8.DefaultSerializer</code></a></li> 1711cb0ef41Sopenharmony_ci<li><a href="#class-v8defaultdeserializer">Class: <code>v8.DefaultDeserializer</code></a></li> 1721cb0ef41Sopenharmony_ci</ul> 1731cb0ef41Sopenharmony_ci</li> 1741cb0ef41Sopenharmony_ci<li><a href="#promise-hooks">Promise hooks</a> 1751cb0ef41Sopenharmony_ci<ul> 1761cb0ef41Sopenharmony_ci<li><a href="#promisehooksoninitinit"><code>promiseHooks.onInit(init)</code></a></li> 1771cb0ef41Sopenharmony_ci<li><a href="#promisehooksonsettledsettled"><code>promiseHooks.onSettled(settled)</code></a></li> 1781cb0ef41Sopenharmony_ci<li><a href="#promisehooksonbeforebefore"><code>promiseHooks.onBefore(before)</code></a></li> 1791cb0ef41Sopenharmony_ci<li><a href="#promisehooksonafterafter"><code>promiseHooks.onAfter(after)</code></a></li> 1801cb0ef41Sopenharmony_ci<li><a href="#promisehookscreatehookcallbacks"><code>promiseHooks.createHook(callbacks)</code></a></li> 1811cb0ef41Sopenharmony_ci<li><a href="#hook-callbacks">Hook callbacks</a> 1821cb0ef41Sopenharmony_ci<ul> 1831cb0ef41Sopenharmony_ci<li><a href="#initpromise-parent"><code>init(promise, parent)</code></a></li> 1841cb0ef41Sopenharmony_ci<li><a href="#beforepromise"><code>before(promise)</code></a></li> 1851cb0ef41Sopenharmony_ci<li><a href="#afterpromise"><code>after(promise)</code></a></li> 1861cb0ef41Sopenharmony_ci<li><a href="#settledpromise"><code>settled(promise)</code></a></li> 1871cb0ef41Sopenharmony_ci</ul> 1881cb0ef41Sopenharmony_ci</li> 1891cb0ef41Sopenharmony_ci</ul> 1901cb0ef41Sopenharmony_ci</li> 1911cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#startup-snapshot-api">Startup Snapshot API</a></span> 1921cb0ef41Sopenharmony_ci<ul> 1931cb0ef41Sopenharmony_ci<li><a href="#v8startupsnapshotaddserializecallbackcallback-data"><code>v8.startupSnapshot.addSerializeCallback(callback[, data])</code></a></li> 1941cb0ef41Sopenharmony_ci<li><a href="#v8startupsnapshotadddeserializecallbackcallback-data"><code>v8.startupSnapshot.addDeserializeCallback(callback[, data])</code></a></li> 1951cb0ef41Sopenharmony_ci<li><a href="#v8startupsnapshotsetdeserializemainfunctioncallback-data"><code>v8.startupSnapshot.setDeserializeMainFunction(callback[, data])</code></a></li> 1961cb0ef41Sopenharmony_ci<li><a href="#v8startupsnapshotisbuildingsnapshot"><code>v8.startupSnapshot.isBuildingSnapshot()</code></a></li> 1971cb0ef41Sopenharmony_ci</ul> 1981cb0ef41Sopenharmony_ci</li> 1991cb0ef41Sopenharmony_ci<li><a href="#class-v8gcprofiler">Class: <code>v8.GCProfiler</code></a> 2001cb0ef41Sopenharmony_ci<ul> 2011cb0ef41Sopenharmony_ci<li><a href="#new-v8gcprofiler"><code>new v8.GCProfiler()</code></a></li> 2021cb0ef41Sopenharmony_ci<li><a href="#profilerstart"><code>profiler.start()</code></a></li> 2031cb0ef41Sopenharmony_ci<li><a href="#profilerstop"><code>profiler.stop()</code></a></li> 2041cb0ef41Sopenharmony_ci</ul> 2051cb0ef41Sopenharmony_ci</li> 2061cb0ef41Sopenharmony_ci</ul> 2071cb0ef41Sopenharmony_ci</li> 2081cb0ef41Sopenharmony_ci</ul></div></div> 2091cb0ef41Sopenharmony_ci </li> 2101cb0ef41Sopenharmony_ci 2111cb0ef41Sopenharmony_ci 2121cb0ef41Sopenharmony_ci <li class="picker-header"> 2131cb0ef41Sopenharmony_ci <a href="#"> 2141cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 2151cb0ef41Sopenharmony_ci Index 2161cb0ef41Sopenharmony_ci </a> 2171cb0ef41Sopenharmony_ci 2181cb0ef41Sopenharmony_ci <div class="picker"><ul> 2191cb0ef41Sopenharmony_ci<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> 2201cb0ef41Sopenharmony_ci<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> 2211cb0ef41Sopenharmony_ci 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2901cb0ef41Sopenharmony_ci<hr class="line"> 2911cb0ef41Sopenharmony_ci<ul> 2921cb0ef41Sopenharmony_ci<li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> 2931cb0ef41Sopenharmony_ci</ul></div> 2941cb0ef41Sopenharmony_ci </li> 2951cb0ef41Sopenharmony_ci 2961cb0ef41Sopenharmony_ci 2971cb0ef41Sopenharmony_ci <li class="picker-header"> 2981cb0ef41Sopenharmony_ci <a href="#"> 2991cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 3001cb0ef41Sopenharmony_ci Other versions 3011cb0ef41Sopenharmony_ci </a> 3021cb0ef41Sopenharmony_ci <div class="picker"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v21.x/api/v8.html">21.x</a></li> 3031cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v20.x/api/v8.html">20.x <b>LTS</b></a></li> 3041cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v19.x/api/v8.html">19.x</a></li> 3051cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v18.x/api/v8.html">18.x <b>LTS</b></a></li> 3061cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v17.x/api/v8.html">17.x</a></li> 3071cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v16.x/api/v8.html">16.x</a></li> 3081cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v15.x/api/v8.html">15.x</a></li> 3091cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v14.x/api/v8.html">14.x</a></li> 3101cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v13.x/api/v8.html">13.x</a></li> 3111cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v12.x/api/v8.html">12.x</a></li> 3121cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v11.x/api/v8.html">11.x</a></li> 3131cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v10.x/api/v8.html">10.x</a></li> 3141cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v9.x/api/v8.html">9.x</a></li> 3151cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v8.x/api/v8.html">8.x</a></li> 3161cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v7.x/api/v8.html">7.x</a></li> 3171cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v6.x/api/v8.html">6.x</a></li> 3181cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v5.x/api/v8.html">5.x</a></li> 3191cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v4.x/api/v8.html">4.x</a></li></ol></div> 3201cb0ef41Sopenharmony_ci </li> 3211cb0ef41Sopenharmony_ci 3221cb0ef41Sopenharmony_ci <li class="picker-header"> 3231cb0ef41Sopenharmony_ci <a href="#"> 3241cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 3251cb0ef41Sopenharmony_ci Options 3261cb0ef41Sopenharmony_ci </a> 3271cb0ef41Sopenharmony_ci 3281cb0ef41Sopenharmony_ci <div class="picker"> 3291cb0ef41Sopenharmony_ci <ul> 3301cb0ef41Sopenharmony_ci <li> 3311cb0ef41Sopenharmony_ci <a href="all.html">View on single page</a> 3321cb0ef41Sopenharmony_ci </li> 3331cb0ef41Sopenharmony_ci <li> 3341cb0ef41Sopenharmony_ci <a href="v8.json">View as JSON</a> 3351cb0ef41Sopenharmony_ci </li> 3361cb0ef41Sopenharmony_ci <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/v8.md">Edit on GitHub</a></li> 3371cb0ef41Sopenharmony_ci </ul> 3381cb0ef41Sopenharmony_ci </div> 3391cb0ef41Sopenharmony_ci </li> 3401cb0ef41Sopenharmony_ci </ul> 3411cb0ef41Sopenharmony_ci </div> 3421cb0ef41Sopenharmony_ci <hr> 3431cb0ef41Sopenharmony_ci </header> 3441cb0ef41Sopenharmony_ci 3451cb0ef41Sopenharmony_ci <details id="toc" open><summary>Table of contents</summary><ul> 3461cb0ef41Sopenharmony_ci<li><a href="#v8">V8</a> 3471cb0ef41Sopenharmony_ci<ul> 3481cb0ef41Sopenharmony_ci<li><a href="#v8cacheddataversiontag"><code>v8.cachedDataVersionTag()</code></a></li> 3491cb0ef41Sopenharmony_ci<li><a href="#v8getheapcodestatistics"><code>v8.getHeapCodeStatistics()</code></a></li> 3501cb0ef41Sopenharmony_ci<li><a href="#v8getheapsnapshot"><code>v8.getHeapSnapshot()</code></a></li> 3511cb0ef41Sopenharmony_ci<li><a href="#v8getheapspacestatistics"><code>v8.getHeapSpaceStatistics()</code></a></li> 3521cb0ef41Sopenharmony_ci<li><a href="#v8getheapstatistics"><code>v8.getHeapStatistics()</code></a></li> 3531cb0ef41Sopenharmony_ci<li><a href="#v8setflagsfromstringflags"><code>v8.setFlagsFromString(flags)</code></a></li> 3541cb0ef41Sopenharmony_ci<li><a href="#v8stopcoverage"><code>v8.stopCoverage()</code></a></li> 3551cb0ef41Sopenharmony_ci<li><a href="#v8takecoverage"><code>v8.takeCoverage()</code></a></li> 3561cb0ef41Sopenharmony_ci<li><a href="#v8writeheapsnapshotfilename"><code>v8.writeHeapSnapshot([filename])</code></a></li> 3571cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#v8setheapsnapshotnearheaplimitlimit"><code>v8.setHeapSnapshotNearHeapLimit(limit)</code></a></span></li> 3581cb0ef41Sopenharmony_ci<li><a href="#serialization-api">Serialization API</a> 3591cb0ef41Sopenharmony_ci<ul> 3601cb0ef41Sopenharmony_ci<li><a href="#v8serializevalue"><code>v8.serialize(value)</code></a></li> 3611cb0ef41Sopenharmony_ci<li><a href="#v8deserializebuffer"><code>v8.deserialize(buffer)</code></a></li> 3621cb0ef41Sopenharmony_ci<li><a href="#class-v8serializer">Class: <code>v8.Serializer</code></a> 3631cb0ef41Sopenharmony_ci<ul> 3641cb0ef41Sopenharmony_ci<li><a href="#new-serializer"><code>new Serializer()</code></a></li> 3651cb0ef41Sopenharmony_ci<li><a href="#serializerwriteheader"><code>serializer.writeHeader()</code></a></li> 3661cb0ef41Sopenharmony_ci<li><a href="#serializerwritevaluevalue"><code>serializer.writeValue(value)</code></a></li> 3671cb0ef41Sopenharmony_ci<li><a href="#serializerreleasebuffer"><code>serializer.releaseBuffer()</code></a></li> 3681cb0ef41Sopenharmony_ci<li><a href="#serializertransferarraybufferid-arraybuffer"><code>serializer.transferArrayBuffer(id, arrayBuffer)</code></a></li> 3691cb0ef41Sopenharmony_ci<li><a href="#serializerwriteuint32value"><code>serializer.writeUint32(value)</code></a></li> 3701cb0ef41Sopenharmony_ci<li><a href="#serializerwriteuint64hi-lo"><code>serializer.writeUint64(hi, lo)</code></a></li> 3711cb0ef41Sopenharmony_ci<li><a href="#serializerwritedoublevalue"><code>serializer.writeDouble(value)</code></a></li> 3721cb0ef41Sopenharmony_ci<li><a href="#serializerwriterawbytesbuffer"><code>serializer.writeRawBytes(buffer)</code></a></li> 3731cb0ef41Sopenharmony_ci<li><a href="#serializer_writehostobjectobject"><code>serializer._writeHostObject(object)</code></a></li> 3741cb0ef41Sopenharmony_ci<li><a href="#serializer_getdatacloneerrormessage"><code>serializer._getDataCloneError(message)</code></a></li> 3751cb0ef41Sopenharmony_ci<li><a href="#serializer_getsharedarraybufferidsharedarraybuffer"><code>serializer._getSharedArrayBufferId(sharedArrayBuffer)</code></a></li> 3761cb0ef41Sopenharmony_ci<li><a href="#serializer_settreatarraybufferviewsashostobjectsflag"><code>serializer._setTreatArrayBufferViewsAsHostObjects(flag)</code></a></li> 3771cb0ef41Sopenharmony_ci</ul> 3781cb0ef41Sopenharmony_ci</li> 3791cb0ef41Sopenharmony_ci<li><a href="#class-v8deserializer">Class: <code>v8.Deserializer</code></a> 3801cb0ef41Sopenharmony_ci<ul> 3811cb0ef41Sopenharmony_ci<li><a href="#new-deserializerbuffer"><code>new Deserializer(buffer)</code></a></li> 3821cb0ef41Sopenharmony_ci<li><a href="#deserializerreadheader"><code>deserializer.readHeader()</code></a></li> 3831cb0ef41Sopenharmony_ci<li><a href="#deserializerreadvalue"><code>deserializer.readValue()</code></a></li> 3841cb0ef41Sopenharmony_ci<li><a href="#deserializertransferarraybufferid-arraybuffer"><code>deserializer.transferArrayBuffer(id, arrayBuffer)</code></a></li> 3851cb0ef41Sopenharmony_ci<li><a href="#deserializergetwireformatversion"><code>deserializer.getWireFormatVersion()</code></a></li> 3861cb0ef41Sopenharmony_ci<li><a href="#deserializerreaduint32"><code>deserializer.readUint32()</code></a></li> 3871cb0ef41Sopenharmony_ci<li><a href="#deserializerreaduint64"><code>deserializer.readUint64()</code></a></li> 3881cb0ef41Sopenharmony_ci<li><a href="#deserializerreaddouble"><code>deserializer.readDouble()</code></a></li> 3891cb0ef41Sopenharmony_ci<li><a href="#deserializerreadrawbyteslength"><code>deserializer.readRawBytes(length)</code></a></li> 3901cb0ef41Sopenharmony_ci<li><a href="#deserializer_readhostobject"><code>deserializer._readHostObject()</code></a></li> 3911cb0ef41Sopenharmony_ci</ul> 3921cb0ef41Sopenharmony_ci</li> 3931cb0ef41Sopenharmony_ci<li><a href="#class-v8defaultserializer">Class: <code>v8.DefaultSerializer</code></a></li> 3941cb0ef41Sopenharmony_ci<li><a href="#class-v8defaultdeserializer">Class: <code>v8.DefaultDeserializer</code></a></li> 3951cb0ef41Sopenharmony_ci</ul> 3961cb0ef41Sopenharmony_ci</li> 3971cb0ef41Sopenharmony_ci<li><a href="#promise-hooks">Promise hooks</a> 3981cb0ef41Sopenharmony_ci<ul> 3991cb0ef41Sopenharmony_ci<li><a href="#promisehooksoninitinit"><code>promiseHooks.onInit(init)</code></a></li> 4001cb0ef41Sopenharmony_ci<li><a href="#promisehooksonsettledsettled"><code>promiseHooks.onSettled(settled)</code></a></li> 4011cb0ef41Sopenharmony_ci<li><a href="#promisehooksonbeforebefore"><code>promiseHooks.onBefore(before)</code></a></li> 4021cb0ef41Sopenharmony_ci<li><a href="#promisehooksonafterafter"><code>promiseHooks.onAfter(after)</code></a></li> 4031cb0ef41Sopenharmony_ci<li><a href="#promisehookscreatehookcallbacks"><code>promiseHooks.createHook(callbacks)</code></a></li> 4041cb0ef41Sopenharmony_ci<li><a href="#hook-callbacks">Hook callbacks</a> 4051cb0ef41Sopenharmony_ci<ul> 4061cb0ef41Sopenharmony_ci<li><a href="#initpromise-parent"><code>init(promise, parent)</code></a></li> 4071cb0ef41Sopenharmony_ci<li><a href="#beforepromise"><code>before(promise)</code></a></li> 4081cb0ef41Sopenharmony_ci<li><a href="#afterpromise"><code>after(promise)</code></a></li> 4091cb0ef41Sopenharmony_ci<li><a href="#settledpromise"><code>settled(promise)</code></a></li> 4101cb0ef41Sopenharmony_ci</ul> 4111cb0ef41Sopenharmony_ci</li> 4121cb0ef41Sopenharmony_ci</ul> 4131cb0ef41Sopenharmony_ci</li> 4141cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#startup-snapshot-api">Startup Snapshot API</a></span> 4151cb0ef41Sopenharmony_ci<ul> 4161cb0ef41Sopenharmony_ci<li><a href="#v8startupsnapshotaddserializecallbackcallback-data"><code>v8.startupSnapshot.addSerializeCallback(callback[, data])</code></a></li> 4171cb0ef41Sopenharmony_ci<li><a href="#v8startupsnapshotadddeserializecallbackcallback-data"><code>v8.startupSnapshot.addDeserializeCallback(callback[, data])</code></a></li> 4181cb0ef41Sopenharmony_ci<li><a href="#v8startupsnapshotsetdeserializemainfunctioncallback-data"><code>v8.startupSnapshot.setDeserializeMainFunction(callback[, data])</code></a></li> 4191cb0ef41Sopenharmony_ci<li><a href="#v8startupsnapshotisbuildingsnapshot"><code>v8.startupSnapshot.isBuildingSnapshot()</code></a></li> 4201cb0ef41Sopenharmony_ci</ul> 4211cb0ef41Sopenharmony_ci</li> 4221cb0ef41Sopenharmony_ci<li><a href="#class-v8gcprofiler">Class: <code>v8.GCProfiler</code></a> 4231cb0ef41Sopenharmony_ci<ul> 4241cb0ef41Sopenharmony_ci<li><a href="#new-v8gcprofiler"><code>new v8.GCProfiler()</code></a></li> 4251cb0ef41Sopenharmony_ci<li><a href="#profilerstart"><code>profiler.start()</code></a></li> 4261cb0ef41Sopenharmony_ci<li><a href="#profilerstop"><code>profiler.stop()</code></a></li> 4271cb0ef41Sopenharmony_ci</ul> 4281cb0ef41Sopenharmony_ci</li> 4291cb0ef41Sopenharmony_ci</ul> 4301cb0ef41Sopenharmony_ci</li> 4311cb0ef41Sopenharmony_ci</ul></details> 4321cb0ef41Sopenharmony_ci 4331cb0ef41Sopenharmony_ci <div id="apicontent"> 4341cb0ef41Sopenharmony_ci <h2>V8<span><a class="mark" href="#v8" id="v8">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8"></a></h2> 4351cb0ef41Sopenharmony_ci 4361cb0ef41Sopenharmony_ci<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v18.20.1/lib/v8.js">lib/v8.js</a></p> 4371cb0ef41Sopenharmony_ci<p>The <code>node:v8</code> module exposes APIs that are specific to the version of <a href="https://developers.google.com/v8/">V8</a> 4381cb0ef41Sopenharmony_cibuilt into the Node.js binary. It can be accessed using:</p> 4391cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> v8 = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>);</code> <button class="copy-button">copy</button></pre> 4401cb0ef41Sopenharmony_ci<section><h3><code>v8.cachedDataVersionTag()</code><span><a class="mark" href="#v8cacheddataversiontag" id="v8cacheddataversiontag">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_cacheddataversiontag"></a></h3> 4411cb0ef41Sopenharmony_ci<div class="api_metadata"> 4421cb0ef41Sopenharmony_ci<span>Added in: v8.0.0</span> 4431cb0ef41Sopenharmony_ci</div> 4441cb0ef41Sopenharmony_ci<ul> 4451cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 4461cb0ef41Sopenharmony_ci</ul> 4471cb0ef41Sopenharmony_ci<p>Returns an integer representing a version tag derived from the V8 version, 4481cb0ef41Sopenharmony_cicommand-line flags, and detected CPU features. This is useful for determining 4491cb0ef41Sopenharmony_ciwhether a <a href="vm.html#new-vmscriptcode-options"><code>vm.Script</code></a> <code>cachedData</code> buffer is compatible with this instance 4501cb0ef41Sopenharmony_ciof V8.</p> 4511cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(v8.<span class="hljs-title function_">cachedDataVersionTag</span>()); <span class="hljs-comment">// 3947234607</span> 4521cb0ef41Sopenharmony_ci<span class="hljs-comment">// The value returned by v8.cachedDataVersionTag() is derived from the V8</span> 4531cb0ef41Sopenharmony_ci<span class="hljs-comment">// version, command-line flags, and detected CPU features. Test that the value</span> 4541cb0ef41Sopenharmony_ci<span class="hljs-comment">// does indeed update when flags are toggled.</span> 4551cb0ef41Sopenharmony_civ8.<span class="hljs-title function_">setFlagsFromString</span>(<span class="hljs-string">'--allow_natives_syntax'</span>); 4561cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(v8.<span class="hljs-title function_">cachedDataVersionTag</span>()); <span class="hljs-comment">// 183726201</span></code> <button class="copy-button">copy</button></pre> 4571cb0ef41Sopenharmony_ci</section><section><h3><code>v8.getHeapCodeStatistics()</code><span><a class="mark" href="#v8getheapcodestatistics" id="v8getheapcodestatistics">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_getheapcodestatistics"></a></h3> 4581cb0ef41Sopenharmony_ci<div class="api_metadata"> 4591cb0ef41Sopenharmony_ci<span>Added in: v12.8.0</span> 4601cb0ef41Sopenharmony_ci</div> 4611cb0ef41Sopenharmony_ci<ul> 4621cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 4631cb0ef41Sopenharmony_ci</ul> 4641cb0ef41Sopenharmony_ci<p>Get statistics about code and its metadata in the heap, see V8 4651cb0ef41Sopenharmony_ci<a href="https://v8docs.nodesource.com/node-13.2/d5/dda/classv8_1_1_isolate.html#a6079122af17612ef54ef3348ce170866"><code>GetHeapCodeAndMetadataStatistics</code></a> API. Returns an object with the 4661cb0ef41Sopenharmony_cifollowing properties:</p> 4671cb0ef41Sopenharmony_ci<ul> 4681cb0ef41Sopenharmony_ci<li><code>code_and_metadata_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 4691cb0ef41Sopenharmony_ci<li><code>bytecode_and_metadata_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 4701cb0ef41Sopenharmony_ci<li><code>external_script_source_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 4711cb0ef41Sopenharmony_ci<li><code>cpu_profiler_metadata_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 4721cb0ef41Sopenharmony_ci</ul> 4731cb0ef41Sopenharmony_ci<!-- eslint-skip --> 4741cb0ef41Sopenharmony_ci<pre><code class="language-js">{ 4751cb0ef41Sopenharmony_ci <span class="hljs-attr">code_and_metadata_size</span>: <span class="hljs-number">212208</span>, 4761cb0ef41Sopenharmony_ci <span class="hljs-attr">bytecode_and_metadata_size</span>: <span class="hljs-number">161368</span>, 4771cb0ef41Sopenharmony_ci <span class="hljs-attr">external_script_source_size</span>: <span class="hljs-number">1410794</span>, 4781cb0ef41Sopenharmony_ci <span class="hljs-attr">cpu_profiler_metadata_size</span>: <span class="hljs-number">0</span>, 4791cb0ef41Sopenharmony_ci}</code> <button class="copy-button">copy</button></pre> 4801cb0ef41Sopenharmony_ci</section><section><h3><code>v8.getHeapSnapshot()</code><span><a class="mark" href="#v8getheapsnapshot" id="v8getheapsnapshot">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_getheapsnapshot"></a></h3> 4811cb0ef41Sopenharmony_ci<div class="api_metadata"> 4821cb0ef41Sopenharmony_ci<span>Added in: v11.13.0</span> 4831cb0ef41Sopenharmony_ci</div> 4841cb0ef41Sopenharmony_ci<ul> 4851cb0ef41Sopenharmony_ci<li>Returns: <a href="stream.html#class-streamreadable" class="type"><stream.Readable></a> A Readable Stream containing the V8 heap snapshot</li> 4861cb0ef41Sopenharmony_ci</ul> 4871cb0ef41Sopenharmony_ci<p>Generates a snapshot of the current V8 heap and returns a Readable 4881cb0ef41Sopenharmony_ciStream that may be used to read the JSON serialized representation. 4891cb0ef41Sopenharmony_ciThis JSON stream format is intended to be used with tools such as 4901cb0ef41Sopenharmony_ciChrome DevTools. The JSON schema is undocumented and specific to the 4911cb0ef41Sopenharmony_ciV8 engine. Therefore, the schema may change from one version of V8 to the next.</p> 4921cb0ef41Sopenharmony_ci<p>Creating a heap snapshot requires memory about twice the size of the heap at 4931cb0ef41Sopenharmony_cithe time the snapshot is created. This results in the risk of OOM killers 4941cb0ef41Sopenharmony_citerminating the process.</p> 4951cb0ef41Sopenharmony_ci<p>Generating a snapshot is a synchronous operation which blocks the event loop 4961cb0ef41Sopenharmony_cifor a duration depending on the heap size.</p> 4971cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-comment">// Print heap snapshot to the console</span> 4981cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> v8 = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 4991cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stream = v8.<span class="hljs-title function_">getHeapSnapshot</span>(); 5001cb0ef41Sopenharmony_cistream.<span class="hljs-title function_">pipe</span>(process.<span class="hljs-property">stdout</span>);</code> <button class="copy-button">copy</button></pre> 5011cb0ef41Sopenharmony_ci</section><section><h3><code>v8.getHeapSpaceStatistics()</code><span><a class="mark" href="#v8getheapspacestatistics" id="v8getheapspacestatistics">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_getheapspacestatistics"></a></h3> 5021cb0ef41Sopenharmony_ci<div class="api_metadata"> 5031cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 5041cb0ef41Sopenharmony_ci<table> 5051cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 5061cb0ef41Sopenharmony_ci<tr><td>v7.5.0</td> 5071cb0ef41Sopenharmony_ci<td><p>Support values exceeding the 32-bit unsigned integer range.</p></td></tr> 5081cb0ef41Sopenharmony_ci<tr><td>v6.0.0</td> 5091cb0ef41Sopenharmony_ci<td><p><span>Added in: v6.0.0</span></p></td></tr> 5101cb0ef41Sopenharmony_ci</tbody></table> 5111cb0ef41Sopenharmony_ci</details> 5121cb0ef41Sopenharmony_ci</div> 5131cb0ef41Sopenharmony_ci<ul> 5141cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object[]></a></li> 5151cb0ef41Sopenharmony_ci</ul> 5161cb0ef41Sopenharmony_ci<p>Returns statistics about the V8 heap spaces, i.e. the segments which make up 5171cb0ef41Sopenharmony_cithe V8 heap. Neither the ordering of heap spaces, nor the availability of a 5181cb0ef41Sopenharmony_ciheap space can be guaranteed as the statistics are provided via the V8 5191cb0ef41Sopenharmony_ci<a href="https://v8docs.nodesource.com/node-13.2/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4"><code>GetHeapSpaceStatistics</code></a> function and may change from one V8 version to the 5201cb0ef41Sopenharmony_cinext.</p> 5211cb0ef41Sopenharmony_ci<p>The value returned is an array of objects containing the following properties:</p> 5221cb0ef41Sopenharmony_ci<ul> 5231cb0ef41Sopenharmony_ci<li><code>space_name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 5241cb0ef41Sopenharmony_ci<li><code>space_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5251cb0ef41Sopenharmony_ci<li><code>space_used_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5261cb0ef41Sopenharmony_ci<li><code>space_available_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5271cb0ef41Sopenharmony_ci<li><code>physical_space_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5281cb0ef41Sopenharmony_ci</ul> 5291cb0ef41Sopenharmony_ci<pre><code class="language-json"><span class="hljs-punctuation">[</span> 5301cb0ef41Sopenharmony_ci <span class="hljs-punctuation">{</span> 5311cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"new_space"</span><span class="hljs-punctuation">,</span> 5321cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">2063872</span><span class="hljs-punctuation">,</span> 5331cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_used_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">951112</span><span class="hljs-punctuation">,</span> 5341cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_available_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">80824</span><span class="hljs-punctuation">,</span> 5351cb0ef41Sopenharmony_ci <span class="hljs-attr">"physical_space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">2063872</span> 5361cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 5371cb0ef41Sopenharmony_ci <span class="hljs-punctuation">{</span> 5381cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"old_space"</span><span class="hljs-punctuation">,</span> 5391cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">3090560</span><span class="hljs-punctuation">,</span> 5401cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_used_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">2493792</span><span class="hljs-punctuation">,</span> 5411cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_available_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 5421cb0ef41Sopenharmony_ci <span class="hljs-attr">"physical_space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">3090560</span> 5431cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 5441cb0ef41Sopenharmony_ci <span class="hljs-punctuation">{</span> 5451cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"code_space"</span><span class="hljs-punctuation">,</span> 5461cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1260160</span><span class="hljs-punctuation">,</span> 5471cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_used_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">644256</span><span class="hljs-punctuation">,</span> 5481cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_available_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">960</span><span class="hljs-punctuation">,</span> 5491cb0ef41Sopenharmony_ci <span class="hljs-attr">"physical_space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1260160</span> 5501cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 5511cb0ef41Sopenharmony_ci <span class="hljs-punctuation">{</span> 5521cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"map_space"</span><span class="hljs-punctuation">,</span> 5531cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1094160</span><span class="hljs-punctuation">,</span> 5541cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_used_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">201608</span><span class="hljs-punctuation">,</span> 5551cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_available_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 5561cb0ef41Sopenharmony_ci <span class="hljs-attr">"physical_space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1094160</span> 5571cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 5581cb0ef41Sopenharmony_ci <span class="hljs-punctuation">{</span> 5591cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"large_object_space"</span><span class="hljs-punctuation">,</span> 5601cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 5611cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_used_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 5621cb0ef41Sopenharmony_ci <span class="hljs-attr">"space_available_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1490980608</span><span class="hljs-punctuation">,</span> 5631cb0ef41Sopenharmony_ci <span class="hljs-attr">"physical_space_size"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span> 5641cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span> 5651cb0ef41Sopenharmony_ci<span class="hljs-punctuation">]</span></code> <button class="copy-button">copy</button></pre> 5661cb0ef41Sopenharmony_ci</section><section><h3><code>v8.getHeapStatistics()</code><span><a class="mark" href="#v8getheapstatistics" id="v8getheapstatistics">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_getheapstatistics"></a></h3> 5671cb0ef41Sopenharmony_ci<div class="api_metadata"> 5681cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 5691cb0ef41Sopenharmony_ci<table> 5701cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 5711cb0ef41Sopenharmony_ci<tr><td>v7.5.0</td> 5721cb0ef41Sopenharmony_ci<td><p>Support values exceeding the 32-bit unsigned integer range.</p></td></tr> 5731cb0ef41Sopenharmony_ci<tr><td>v7.2.0</td> 5741cb0ef41Sopenharmony_ci<td><p>Added <code>malloced_memory</code>, <code>peak_malloced_memory</code>, and <code>does_zap_garbage</code>.</p></td></tr> 5751cb0ef41Sopenharmony_ci<tr><td>v1.0.0</td> 5761cb0ef41Sopenharmony_ci<td><p><span>Added in: v1.0.0</span></p></td></tr> 5771cb0ef41Sopenharmony_ci</tbody></table> 5781cb0ef41Sopenharmony_ci</details> 5791cb0ef41Sopenharmony_ci</div> 5801cb0ef41Sopenharmony_ci<ul> 5811cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 5821cb0ef41Sopenharmony_ci</ul> 5831cb0ef41Sopenharmony_ci<p>Returns an object with the following properties:</p> 5841cb0ef41Sopenharmony_ci<ul> 5851cb0ef41Sopenharmony_ci<li><code>total_heap_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5861cb0ef41Sopenharmony_ci<li><code>total_heap_size_executable</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5871cb0ef41Sopenharmony_ci<li><code>total_physical_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5881cb0ef41Sopenharmony_ci<li><code>total_available_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5891cb0ef41Sopenharmony_ci<li><code>used_heap_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5901cb0ef41Sopenharmony_ci<li><code>heap_size_limit</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5911cb0ef41Sopenharmony_ci<li><code>malloced_memory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5921cb0ef41Sopenharmony_ci<li><code>peak_malloced_memory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5931cb0ef41Sopenharmony_ci<li><code>does_zap_garbage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5941cb0ef41Sopenharmony_ci<li><code>number_of_native_contexts</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5951cb0ef41Sopenharmony_ci<li><code>number_of_detached_contexts</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5961cb0ef41Sopenharmony_ci<li><code>total_global_handles_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5971cb0ef41Sopenharmony_ci<li><code>used_global_handles_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5981cb0ef41Sopenharmony_ci<li><code>external_memory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 5991cb0ef41Sopenharmony_ci</ul> 6001cb0ef41Sopenharmony_ci<p><code>does_zap_garbage</code> is a 0/1 boolean, which signifies whether the 6011cb0ef41Sopenharmony_ci<code>--zap_code_space</code> option is enabled or not. This makes V8 overwrite heap 6021cb0ef41Sopenharmony_cigarbage with a bit pattern. The RSS footprint (resident set size) gets bigger 6031cb0ef41Sopenharmony_cibecause it continuously touches all heap pages and that makes them less likely 6041cb0ef41Sopenharmony_cito get swapped out by the operating system.</p> 6051cb0ef41Sopenharmony_ci<p><code>number_of_native_contexts</code> The value of native_context is the number of the 6061cb0ef41Sopenharmony_citop-level contexts currently active. Increase of this number over time indicates 6071cb0ef41Sopenharmony_cia memory leak.</p> 6081cb0ef41Sopenharmony_ci<p><code>number_of_detached_contexts</code> The value of detached_context is the number 6091cb0ef41Sopenharmony_ciof contexts that were detached and not yet garbage collected. This number 6101cb0ef41Sopenharmony_cibeing non-zero indicates a potential memory leak.</p> 6111cb0ef41Sopenharmony_ci<p><code>total_global_handles_size</code> The value of total_global_handles_size is the 6121cb0ef41Sopenharmony_citotal memory size of V8 global handles.</p> 6131cb0ef41Sopenharmony_ci<p><code>used_global_handles_size</code> The value of used_global_handles_size is the 6141cb0ef41Sopenharmony_ciused memory size of V8 global handles.</p> 6151cb0ef41Sopenharmony_ci<p><code>external_memory</code> The value of external_memory is the memory size of array 6161cb0ef41Sopenharmony_cibuffers and external strings.</p> 6171cb0ef41Sopenharmony_ci<!-- eslint-skip --> 6181cb0ef41Sopenharmony_ci<pre><code class="language-js">{ 6191cb0ef41Sopenharmony_ci <span class="hljs-attr">total_heap_size</span>: <span class="hljs-number">7326976</span>, 6201cb0ef41Sopenharmony_ci <span class="hljs-attr">total_heap_size_executable</span>: <span class="hljs-number">4194304</span>, 6211cb0ef41Sopenharmony_ci <span class="hljs-attr">total_physical_size</span>: <span class="hljs-number">7326976</span>, 6221cb0ef41Sopenharmony_ci <span class="hljs-attr">total_available_size</span>: <span class="hljs-number">1152656</span>, 6231cb0ef41Sopenharmony_ci <span class="hljs-attr">used_heap_size</span>: <span class="hljs-number">3476208</span>, 6241cb0ef41Sopenharmony_ci <span class="hljs-attr">heap_size_limit</span>: <span class="hljs-number">1535115264</span>, 6251cb0ef41Sopenharmony_ci <span class="hljs-attr">malloced_memory</span>: <span class="hljs-number">16384</span>, 6261cb0ef41Sopenharmony_ci <span class="hljs-attr">peak_malloced_memory</span>: <span class="hljs-number">1127496</span>, 6271cb0ef41Sopenharmony_ci <span class="hljs-attr">does_zap_garbage</span>: <span class="hljs-number">0</span>, 6281cb0ef41Sopenharmony_ci <span class="hljs-attr">number_of_native_contexts</span>: <span class="hljs-number">1</span>, 6291cb0ef41Sopenharmony_ci <span class="hljs-attr">number_of_detached_contexts</span>: <span class="hljs-number">0</span>, 6301cb0ef41Sopenharmony_ci <span class="hljs-attr">total_global_handles_size</span>: <span class="hljs-number">8192</span>, 6311cb0ef41Sopenharmony_ci <span class="hljs-attr">used_global_handles_size</span>: <span class="hljs-number">3296</span>, 6321cb0ef41Sopenharmony_ci <span class="hljs-attr">external_memory</span>: <span class="hljs-number">318824</span> 6331cb0ef41Sopenharmony_ci}</code> <button class="copy-button">copy</button></pre> 6341cb0ef41Sopenharmony_ci</section><section><h3><code>v8.setFlagsFromString(flags)</code><span><a class="mark" href="#v8setflagsfromstringflags" id="v8setflagsfromstringflags">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_setflagsfromstring_flags"></a></h3> 6351cb0ef41Sopenharmony_ci<div class="api_metadata"> 6361cb0ef41Sopenharmony_ci<span>Added in: v1.0.0</span> 6371cb0ef41Sopenharmony_ci</div> 6381cb0ef41Sopenharmony_ci<ul> 6391cb0ef41Sopenharmony_ci<li><code>flags</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 6401cb0ef41Sopenharmony_ci</ul> 6411cb0ef41Sopenharmony_ci<p>The <code>v8.setFlagsFromString()</code> method can be used to programmatically set 6421cb0ef41Sopenharmony_ciV8 command-line flags. This method should be used with care. Changing settings 6431cb0ef41Sopenharmony_ciafter the VM has started may result in unpredictable behavior, including 6441cb0ef41Sopenharmony_cicrashes and data loss; or it may simply do nothing.</p> 6451cb0ef41Sopenharmony_ci<p>The V8 options available for a version of Node.js may be determined by running 6461cb0ef41Sopenharmony_ci<code>node --v8-options</code>.</p> 6471cb0ef41Sopenharmony_ci<p>Usage:</p> 6481cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-comment">// Print GC events to stdout for one minute.</span> 6491cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> v8 = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 6501cb0ef41Sopenharmony_civ8.<span class="hljs-title function_">setFlagsFromString</span>(<span class="hljs-string">'--trace_gc'</span>); 6511cb0ef41Sopenharmony_ci<span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { v8.<span class="hljs-title function_">setFlagsFromString</span>(<span class="hljs-string">'--notrace_gc'</span>); }, <span class="hljs-number">60e3</span>);</code> <button class="copy-button">copy</button></pre> 6521cb0ef41Sopenharmony_ci</section><section><h3><code>v8.stopCoverage()</code><span><a class="mark" href="#v8stopcoverage" id="v8stopcoverage">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_stopcoverage"></a></h3> 6531cb0ef41Sopenharmony_ci<div class="api_metadata"> 6541cb0ef41Sopenharmony_ci<span>Added in: v15.1.0, v14.18.0, v12.22.0</span> 6551cb0ef41Sopenharmony_ci</div> 6561cb0ef41Sopenharmony_ci<p>The <code>v8.stopCoverage()</code> method allows the user to stop the coverage collection 6571cb0ef41Sopenharmony_cistarted by <a href="cli.html#node_v8_coveragedir"><code>NODE_V8_COVERAGE</code></a>, so that V8 can release the execution count 6581cb0ef41Sopenharmony_cirecords and optimize code. This can be used in conjunction with 6591cb0ef41Sopenharmony_ci<a href="#v8takecoverage"><code>v8.takeCoverage()</code></a> if the user wants to collect the coverage on demand.</p> 6601cb0ef41Sopenharmony_ci</section><section><h3><code>v8.takeCoverage()</code><span><a class="mark" href="#v8takecoverage" id="v8takecoverage">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_takecoverage"></a></h3> 6611cb0ef41Sopenharmony_ci<div class="api_metadata"> 6621cb0ef41Sopenharmony_ci<span>Added in: v15.1.0, v14.18.0, v12.22.0</span> 6631cb0ef41Sopenharmony_ci</div> 6641cb0ef41Sopenharmony_ci<p>The <code>v8.takeCoverage()</code> method allows the user to write the coverage started by 6651cb0ef41Sopenharmony_ci<a href="cli.html#node_v8_coveragedir"><code>NODE_V8_COVERAGE</code></a> to disk on demand. This method can be invoked multiple 6661cb0ef41Sopenharmony_citimes during the lifetime of the process. Each time the execution counter will 6671cb0ef41Sopenharmony_cibe reset and a new coverage report will be written to the directory specified 6681cb0ef41Sopenharmony_ciby <a href="cli.html#node_v8_coveragedir"><code>NODE_V8_COVERAGE</code></a>.</p> 6691cb0ef41Sopenharmony_ci<p>When the process is about to exit, one last coverage will still be written to 6701cb0ef41Sopenharmony_cidisk unless <a href="#v8stopcoverage"><code>v8.stopCoverage()</code></a> is invoked before the process exits.</p> 6711cb0ef41Sopenharmony_ci</section><section><h3><code>v8.writeHeapSnapshot([filename])</code><span><a class="mark" href="#v8writeheapsnapshotfilename" id="v8writeheapsnapshotfilename">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_writeheapsnapshot_filename"></a></h3> 6721cb0ef41Sopenharmony_ci<div class="api_metadata"> 6731cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 6741cb0ef41Sopenharmony_ci<table> 6751cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 6761cb0ef41Sopenharmony_ci<tr><td>v18.0.0</td> 6771cb0ef41Sopenharmony_ci<td><p>An exception will now be thrown if the file could not be written.</p></td></tr> 6781cb0ef41Sopenharmony_ci<tr><td>v18.0.0</td> 6791cb0ef41Sopenharmony_ci<td><p>Make the returned error codes consistent across all platforms.</p></td></tr> 6801cb0ef41Sopenharmony_ci<tr><td>v11.13.0</td> 6811cb0ef41Sopenharmony_ci<td><p><span>Added in: v11.13.0</span></p></td></tr> 6821cb0ef41Sopenharmony_ci</tbody></table> 6831cb0ef41Sopenharmony_ci</details> 6841cb0ef41Sopenharmony_ci</div> 6851cb0ef41Sopenharmony_ci<ul> 6861cb0ef41Sopenharmony_ci<li><code>filename</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The file path where the V8 heap snapshot is to be 6871cb0ef41Sopenharmony_cisaved. If not specified, a file name with the pattern 6881cb0ef41Sopenharmony_ci<code>'Heap-${yyyymmdd}-${hhmmss}-${pid}-${thread_id}.heapsnapshot'</code> will be 6891cb0ef41Sopenharmony_cigenerated, where <code>{pid}</code> will be the PID of the Node.js process, 6901cb0ef41Sopenharmony_ci<code>{thread_id}</code> will be <code>0</code> when <code>writeHeapSnapshot()</code> is called from 6911cb0ef41Sopenharmony_cithe main Node.js thread or the id of a worker thread.</li> 6921cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The filename where the snapshot was saved.</li> 6931cb0ef41Sopenharmony_ci</ul> 6941cb0ef41Sopenharmony_ci<p>Generates a snapshot of the current V8 heap and writes it to a JSON 6951cb0ef41Sopenharmony_cifile. This file is intended to be used with tools such as Chrome 6961cb0ef41Sopenharmony_ciDevTools. The JSON schema is undocumented and specific to the V8 6971cb0ef41Sopenharmony_ciengine, and may change from one version of V8 to the next.</p> 6981cb0ef41Sopenharmony_ci<p>A heap snapshot is specific to a single V8 isolate. When using 6991cb0ef41Sopenharmony_ci<a href="worker_threads.html">worker threads</a>, a heap snapshot generated from the main thread will 7001cb0ef41Sopenharmony_cinot contain any information about the workers, and vice versa.</p> 7011cb0ef41Sopenharmony_ci<p>Creating a heap snapshot requires memory about twice the size of the heap at 7021cb0ef41Sopenharmony_cithe time the snapshot is created. This results in the risk of OOM killers 7031cb0ef41Sopenharmony_citerminating the process.</p> 7041cb0ef41Sopenharmony_ci<p>Generating a snapshot is a synchronous operation which blocks the event loop 7051cb0ef41Sopenharmony_cifor a duration depending on the heap size.</p> 7061cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> { writeHeapSnapshot } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 7071cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { 7081cb0ef41Sopenharmony_ci <span class="hljs-title class_">Worker</span>, 7091cb0ef41Sopenharmony_ci isMainThread, 7101cb0ef41Sopenharmony_ci parentPort, 7111cb0ef41Sopenharmony_ci} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:worker_threads'</span>); 7121cb0ef41Sopenharmony_ci 7131cb0ef41Sopenharmony_ci<span class="hljs-keyword">if</span> (isMainThread) { 7141cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> worker = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Worker</span>(__filename); 7151cb0ef41Sopenharmony_ci 7161cb0ef41Sopenharmony_ci worker.<span class="hljs-title function_">once</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">filename</span>) =></span> { 7171cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`worker heapdump: <span class="hljs-subst">${filename}</span>`</span>); 7181cb0ef41Sopenharmony_ci <span class="hljs-comment">// Now get a heapdump for the main thread.</span> 7191cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`main thread heapdump: <span class="hljs-subst">${writeHeapSnapshot()}</span>`</span>); 7201cb0ef41Sopenharmony_ci }); 7211cb0ef41Sopenharmony_ci 7221cb0ef41Sopenharmony_ci <span class="hljs-comment">// Tell the worker to create a heapdump.</span> 7231cb0ef41Sopenharmony_ci worker.<span class="hljs-title function_">postMessage</span>(<span class="hljs-string">'heapdump'</span>); 7241cb0ef41Sopenharmony_ci} <span class="hljs-keyword">else</span> { 7251cb0ef41Sopenharmony_ci parentPort.<span class="hljs-title function_">once</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">message</span>) =></span> { 7261cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (message === <span class="hljs-string">'heapdump'</span>) { 7271cb0ef41Sopenharmony_ci <span class="hljs-comment">// Generate a heapdump for the worker</span> 7281cb0ef41Sopenharmony_ci <span class="hljs-comment">// and return the filename to the parent.</span> 7291cb0ef41Sopenharmony_ci parentPort.<span class="hljs-title function_">postMessage</span>(<span class="hljs-title function_">writeHeapSnapshot</span>()); 7301cb0ef41Sopenharmony_ci } 7311cb0ef41Sopenharmony_ci }); 7321cb0ef41Sopenharmony_ci}</code> <button class="copy-button">copy</button></pre> 7331cb0ef41Sopenharmony_ci</section><section><h3><code>v8.setHeapSnapshotNearHeapLimit(limit)</code><span><a class="mark" href="#v8setheapsnapshotnearheaplimitlimit" id="v8setheapsnapshotnearheaplimitlimit">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_setheapsnapshotnearheaplimit_limit"></a></h3> 7341cb0ef41Sopenharmony_ci<div class="api_metadata"> 7351cb0ef41Sopenharmony_ci<span>Added in: v18.10.0</span> 7361cb0ef41Sopenharmony_ci</div> 7371cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 7381cb0ef41Sopenharmony_ci<ul> 7391cb0ef41Sopenharmony_ci<li><code>limit</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 7401cb0ef41Sopenharmony_ci</ul> 7411cb0ef41Sopenharmony_ci<p>The API is a no-op if <code>--heapsnapshot-near-heap-limit</code> is already set from the 7421cb0ef41Sopenharmony_cicommand line or the API is called more than once. <code>limit</code> must be a positive 7431cb0ef41Sopenharmony_ciinteger. See <a href="cli.html#--heapsnapshot-near-heap-limitmax_count"><code>--heapsnapshot-near-heap-limit</code></a> for more information.</p> 7441cb0ef41Sopenharmony_ci</section><section><h3>Serialization API<span><a class="mark" href="#serialization-api" id="serialization-api">#</a></span><a aria-hidden="true" class="legacy" id="v8_serialization_api"></a></h3> 7451cb0ef41Sopenharmony_ci<p>The serialization API provides means of serializing JavaScript values in a way 7461cb0ef41Sopenharmony_cithat is compatible with the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm">HTML structured clone algorithm</a>.</p> 7471cb0ef41Sopenharmony_ci<p>The format is backward-compatible (i.e. safe to store to disk). 7481cb0ef41Sopenharmony_ciEqual JavaScript values may result in different serialized output.</p> 7491cb0ef41Sopenharmony_ci<h4><code>v8.serialize(value)</code><span><a class="mark" href="#v8serializevalue" id="v8serializevalue">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_serialize_value"></a></h4> 7501cb0ef41Sopenharmony_ci<div class="api_metadata"> 7511cb0ef41Sopenharmony_ci<span>Added in: v8.0.0</span> 7521cb0ef41Sopenharmony_ci</div> 7531cb0ef41Sopenharmony_ci<ul> 7541cb0ef41Sopenharmony_ci<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 7551cb0ef41Sopenharmony_ci<li>Returns: <a href="buffer.html#class-buffer" class="type"><Buffer></a></li> 7561cb0ef41Sopenharmony_ci</ul> 7571cb0ef41Sopenharmony_ci<p>Uses a <a href="#class-v8defaultserializer"><code>DefaultSerializer</code></a> to serialize <code>value</code> into a buffer.</p> 7581cb0ef41Sopenharmony_ci<p><a href="errors.html#err_buffer_too_large"><code>ERR_BUFFER_TOO_LARGE</code></a> will be thrown when trying to 7591cb0ef41Sopenharmony_ciserialize a huge object which requires buffer 7601cb0ef41Sopenharmony_cilarger than <a href="buffer.html#bufferconstantsmax_length"><code>buffer.constants.MAX_LENGTH</code></a>.</p> 7611cb0ef41Sopenharmony_ci<h4><code>v8.deserialize(buffer)</code><span><a class="mark" href="#v8deserializebuffer" id="v8deserializebuffer">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_deserialize_buffer"></a></h4> 7621cb0ef41Sopenharmony_ci<div class="api_metadata"> 7631cb0ef41Sopenharmony_ci<span>Added in: v8.0.0</span> 7641cb0ef41Sopenharmony_ci</div> 7651cb0ef41Sopenharmony_ci<ul> 7661cb0ef41Sopenharmony_ci<li><code>buffer</code> <a href="buffer.html#class-buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a> A buffer returned by <a href="#v8serializevalue"><code>serialize()</code></a>.</li> 7671cb0ef41Sopenharmony_ci</ul> 7681cb0ef41Sopenharmony_ci<p>Uses a <a href="#class-v8defaultdeserializer"><code>DefaultDeserializer</code></a> with default options to read a JS value 7691cb0ef41Sopenharmony_cifrom a buffer.</p> 7701cb0ef41Sopenharmony_ci<h4>Class: <code>v8.Serializer</code><span><a class="mark" href="#class-v8serializer" id="class-v8serializer">#</a></span><a aria-hidden="true" class="legacy" id="v8_class_v8_serializer"></a></h4> 7711cb0ef41Sopenharmony_ci<div class="api_metadata"> 7721cb0ef41Sopenharmony_ci<span>Added in: v8.0.0</span> 7731cb0ef41Sopenharmony_ci</div> 7741cb0ef41Sopenharmony_ci<h5><code>new Serializer()</code><span><a class="mark" href="#new-serializer" id="new-serializer">#</a></span><a aria-hidden="true" class="legacy" id="v8_new_serializer"></a></h5> 7751cb0ef41Sopenharmony_ci<p>Creates a new <code>Serializer</code> object.</p> 7761cb0ef41Sopenharmony_ci<h5><code>serializer.writeHeader()</code><span><a class="mark" href="#serializerwriteheader" id="serializerwriteheader">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_writeheader"></a></h5> 7771cb0ef41Sopenharmony_ci<p>Writes out a header, which includes the serialization format version.</p> 7781cb0ef41Sopenharmony_ci<h5><code>serializer.writeValue(value)</code><span><a class="mark" href="#serializerwritevaluevalue" id="serializerwritevaluevalue">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_writevalue_value"></a></h5> 7791cb0ef41Sopenharmony_ci<ul> 7801cb0ef41Sopenharmony_ci<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 7811cb0ef41Sopenharmony_ci</ul> 7821cb0ef41Sopenharmony_ci<p>Serializes a JavaScript value and adds the serialized representation to the 7831cb0ef41Sopenharmony_ciinternal buffer.</p> 7841cb0ef41Sopenharmony_ci<p>This throws an error if <code>value</code> cannot be serialized.</p> 7851cb0ef41Sopenharmony_ci<h5><code>serializer.releaseBuffer()</code><span><a class="mark" href="#serializerreleasebuffer" id="serializerreleasebuffer">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_releasebuffer"></a></h5> 7861cb0ef41Sopenharmony_ci<ul> 7871cb0ef41Sopenharmony_ci<li>Returns: <a href="buffer.html#class-buffer" class="type"><Buffer></a></li> 7881cb0ef41Sopenharmony_ci</ul> 7891cb0ef41Sopenharmony_ci<p>Returns the stored internal buffer. This serializer should not be used once 7901cb0ef41Sopenharmony_cithe buffer is released. Calling this method results in undefined behavior 7911cb0ef41Sopenharmony_ciif a previous write has failed.</p> 7921cb0ef41Sopenharmony_ci<h5><code>serializer.transferArrayBuffer(id, arrayBuffer)</code><span><a class="mark" href="#serializertransferarraybufferid-arraybuffer" id="serializertransferarraybufferid-arraybuffer">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_transferarraybuffer_id_arraybuffer"></a></h5> 7931cb0ef41Sopenharmony_ci<ul> 7941cb0ef41Sopenharmony_ci<li><code>id</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> A 32-bit unsigned integer.</li> 7951cb0ef41Sopenharmony_ci<li><code>arrayBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> An <code>ArrayBuffer</code> instance.</li> 7961cb0ef41Sopenharmony_ci</ul> 7971cb0ef41Sopenharmony_ci<p>Marks an <code>ArrayBuffer</code> as having its contents transferred out of band. 7981cb0ef41Sopenharmony_ciPass the corresponding <code>ArrayBuffer</code> in the deserializing context to 7991cb0ef41Sopenharmony_ci<a href="#deserializertransferarraybufferid-arraybuffer"><code>deserializer.transferArrayBuffer()</code></a>.</p> 8001cb0ef41Sopenharmony_ci<h5><code>serializer.writeUint32(value)</code><span><a class="mark" href="#serializerwriteuint32value" id="serializerwriteuint32value">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_writeuint32_value"></a></h5> 8011cb0ef41Sopenharmony_ci<ul> 8021cb0ef41Sopenharmony_ci<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 8031cb0ef41Sopenharmony_ci</ul> 8041cb0ef41Sopenharmony_ci<p>Write a raw 32-bit unsigned integer. 8051cb0ef41Sopenharmony_ciFor use inside of a custom <a href="#serializer_writehostobjectobject"><code>serializer._writeHostObject()</code></a>.</p> 8061cb0ef41Sopenharmony_ci<h5><code>serializer.writeUint64(hi, lo)</code><span><a class="mark" href="#serializerwriteuint64hi-lo" id="serializerwriteuint64hi-lo">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_writeuint64_hi_lo"></a></h5> 8071cb0ef41Sopenharmony_ci<ul> 8081cb0ef41Sopenharmony_ci<li><code>hi</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 8091cb0ef41Sopenharmony_ci<li><code>lo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 8101cb0ef41Sopenharmony_ci</ul> 8111cb0ef41Sopenharmony_ci<p>Write a raw 64-bit unsigned integer, split into high and low 32-bit parts. 8121cb0ef41Sopenharmony_ciFor use inside of a custom <a href="#serializer_writehostobjectobject"><code>serializer._writeHostObject()</code></a>.</p> 8131cb0ef41Sopenharmony_ci<h5><code>serializer.writeDouble(value)</code><span><a class="mark" href="#serializerwritedoublevalue" id="serializerwritedoublevalue">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_writedouble_value"></a></h5> 8141cb0ef41Sopenharmony_ci<ul> 8151cb0ef41Sopenharmony_ci<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 8161cb0ef41Sopenharmony_ci</ul> 8171cb0ef41Sopenharmony_ci<p>Write a JS <code>number</code> value. 8181cb0ef41Sopenharmony_ciFor use inside of a custom <a href="#serializer_writehostobjectobject"><code>serializer._writeHostObject()</code></a>.</p> 8191cb0ef41Sopenharmony_ci<h5><code>serializer.writeRawBytes(buffer)</code><span><a class="mark" href="#serializerwriterawbytesbuffer" id="serializerwriterawbytesbuffer">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_writerawbytes_buffer"></a></h5> 8201cb0ef41Sopenharmony_ci<ul> 8211cb0ef41Sopenharmony_ci<li><code>buffer</code> <a href="buffer.html#class-buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a></li> 8221cb0ef41Sopenharmony_ci</ul> 8231cb0ef41Sopenharmony_ci<p>Write raw bytes into the serializer's internal buffer. The deserializer 8241cb0ef41Sopenharmony_ciwill require a way to compute the length of the buffer. 8251cb0ef41Sopenharmony_ciFor use inside of a custom <a href="#serializer_writehostobjectobject"><code>serializer._writeHostObject()</code></a>.</p> 8261cb0ef41Sopenharmony_ci<h5><code>serializer._writeHostObject(object)</code><span><a class="mark" href="#serializer_writehostobjectobject" id="serializer_writehostobjectobject">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_writehostobject_object"></a></h5> 8271cb0ef41Sopenharmony_ci<ul> 8281cb0ef41Sopenharmony_ci<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 8291cb0ef41Sopenharmony_ci</ul> 8301cb0ef41Sopenharmony_ci<p>This method is called to write some kind of host object, i.e. an object created 8311cb0ef41Sopenharmony_ciby native C++ bindings. If it is not possible to serialize <code>object</code>, a suitable 8321cb0ef41Sopenharmony_ciexception should be thrown.</p> 8331cb0ef41Sopenharmony_ci<p>This method is not present on the <code>Serializer</code> class itself but can be provided 8341cb0ef41Sopenharmony_ciby subclasses.</p> 8351cb0ef41Sopenharmony_ci<h5><code>serializer._getDataCloneError(message)</code><span><a class="mark" href="#serializer_getdatacloneerrormessage" id="serializer_getdatacloneerrormessage">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_getdatacloneerror_message"></a></h5> 8361cb0ef41Sopenharmony_ci<ul> 8371cb0ef41Sopenharmony_ci<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 8381cb0ef41Sopenharmony_ci</ul> 8391cb0ef41Sopenharmony_ci<p>This method is called to generate error objects that will be thrown when an 8401cb0ef41Sopenharmony_ciobject can not be cloned.</p> 8411cb0ef41Sopenharmony_ci<p>This method defaults to the <a href="errors.html#class-error"><code>Error</code></a> constructor and can be overridden on 8421cb0ef41Sopenharmony_cisubclasses.</p> 8431cb0ef41Sopenharmony_ci<h5><code>serializer._getSharedArrayBufferId(sharedArrayBuffer)</code><span><a class="mark" href="#serializer_getsharedarraybufferidsharedarraybuffer" id="serializer_getsharedarraybufferidsharedarraybuffer">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_getsharedarraybufferid_sharedarraybuffer"></a></h5> 8441cb0ef41Sopenharmony_ci<ul> 8451cb0ef41Sopenharmony_ci<li><code>sharedArrayBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer" class="type"><SharedArrayBuffer></a></li> 8461cb0ef41Sopenharmony_ci</ul> 8471cb0ef41Sopenharmony_ci<p>This method is called when the serializer is going to serialize a 8481cb0ef41Sopenharmony_ci<code>SharedArrayBuffer</code> object. It must return an unsigned 32-bit integer ID for 8491cb0ef41Sopenharmony_cithe object, using the same ID if this <code>SharedArrayBuffer</code> has already been 8501cb0ef41Sopenharmony_ciserialized. When deserializing, this ID will be passed to 8511cb0ef41Sopenharmony_ci<a href="#deserializertransferarraybufferid-arraybuffer"><code>deserializer.transferArrayBuffer()</code></a>.</p> 8521cb0ef41Sopenharmony_ci<p>If the object cannot be serialized, an exception should be thrown.</p> 8531cb0ef41Sopenharmony_ci<p>This method is not present on the <code>Serializer</code> class itself but can be provided 8541cb0ef41Sopenharmony_ciby subclasses.</p> 8551cb0ef41Sopenharmony_ci<h5><code>serializer._setTreatArrayBufferViewsAsHostObjects(flag)</code><span><a class="mark" href="#serializer_settreatarraybufferviewsashostobjectsflag" id="serializer_settreatarraybufferviewsashostobjectsflag">#</a></span><a aria-hidden="true" class="legacy" id="v8_serializer_settreatarraybufferviewsashostobjects_flag"></a></h5> 8561cb0ef41Sopenharmony_ci<ul> 8571cb0ef41Sopenharmony_ci<li><code>flag</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <strong>Default:</strong> <code>false</code></li> 8581cb0ef41Sopenharmony_ci</ul> 8591cb0ef41Sopenharmony_ci<p>Indicate whether to treat <code>TypedArray</code> and <code>DataView</code> objects as 8601cb0ef41Sopenharmony_cihost objects, i.e. pass them to <a href="#serializer_writehostobjectobject"><code>serializer._writeHostObject()</code></a>.</p> 8611cb0ef41Sopenharmony_ci<h4>Class: <code>v8.Deserializer</code><span><a class="mark" href="#class-v8deserializer" id="class-v8deserializer">#</a></span><a aria-hidden="true" class="legacy" id="v8_class_v8_deserializer"></a></h4> 8621cb0ef41Sopenharmony_ci<div class="api_metadata"> 8631cb0ef41Sopenharmony_ci<span>Added in: v8.0.0</span> 8641cb0ef41Sopenharmony_ci</div> 8651cb0ef41Sopenharmony_ci<h5><code>new Deserializer(buffer)</code><span><a class="mark" href="#new-deserializerbuffer" id="new-deserializerbuffer">#</a></span><a aria-hidden="true" class="legacy" id="v8_new_deserializer_buffer"></a></h5> 8661cb0ef41Sopenharmony_ci<ul> 8671cb0ef41Sopenharmony_ci<li><code>buffer</code> <a href="buffer.html#class-buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a> A buffer returned by 8681cb0ef41Sopenharmony_ci<a href="#serializerreleasebuffer"><code>serializer.releaseBuffer()</code></a>.</li> 8691cb0ef41Sopenharmony_ci</ul> 8701cb0ef41Sopenharmony_ci<p>Creates a new <code>Deserializer</code> object.</p> 8711cb0ef41Sopenharmony_ci<h5><code>deserializer.readHeader()</code><span><a class="mark" href="#deserializerreadheader" id="deserializerreadheader">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_readheader"></a></h5> 8721cb0ef41Sopenharmony_ci<p>Reads and validates a header (including the format version). 8731cb0ef41Sopenharmony_ciMay, for example, reject an invalid or unsupported wire format. In that case, 8741cb0ef41Sopenharmony_cian <code>Error</code> is thrown.</p> 8751cb0ef41Sopenharmony_ci<h5><code>deserializer.readValue()</code><span><a class="mark" href="#deserializerreadvalue" id="deserializerreadvalue">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_readvalue"></a></h5> 8761cb0ef41Sopenharmony_ci<p>Deserializes a JavaScript value from the buffer and returns it.</p> 8771cb0ef41Sopenharmony_ci<h5><code>deserializer.transferArrayBuffer(id, arrayBuffer)</code><span><a class="mark" href="#deserializertransferarraybufferid-arraybuffer" id="deserializertransferarraybufferid-arraybuffer">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_transferarraybuffer_id_arraybuffer"></a></h5> 8781cb0ef41Sopenharmony_ci<ul> 8791cb0ef41Sopenharmony_ci<li><code>id</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> A 32-bit unsigned integer.</li> 8801cb0ef41Sopenharmony_ci<li><code>arrayBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer" class="type"><SharedArrayBuffer></a> An <code>ArrayBuffer</code> instance.</li> 8811cb0ef41Sopenharmony_ci</ul> 8821cb0ef41Sopenharmony_ci<p>Marks an <code>ArrayBuffer</code> as having its contents transferred out of band. 8831cb0ef41Sopenharmony_ciPass the corresponding <code>ArrayBuffer</code> in the serializing context to 8841cb0ef41Sopenharmony_ci<a href="#serializertransferarraybufferid-arraybuffer"><code>serializer.transferArrayBuffer()</code></a> (or return the <code>id</code> from 8851cb0ef41Sopenharmony_ci<a href="#serializer_getsharedarraybufferidsharedarraybuffer"><code>serializer._getSharedArrayBufferId()</code></a> in the case of <code>SharedArrayBuffer</code>s).</p> 8861cb0ef41Sopenharmony_ci<h5><code>deserializer.getWireFormatVersion()</code><span><a class="mark" href="#deserializergetwireformatversion" id="deserializergetwireformatversion">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_getwireformatversion"></a></h5> 8871cb0ef41Sopenharmony_ci<ul> 8881cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 8891cb0ef41Sopenharmony_ci</ul> 8901cb0ef41Sopenharmony_ci<p>Reads the underlying wire format version. Likely mostly to be useful to 8911cb0ef41Sopenharmony_cilegacy code reading old wire format versions. May not be called before 8921cb0ef41Sopenharmony_ci<code>.readHeader()</code>.</p> 8931cb0ef41Sopenharmony_ci<h5><code>deserializer.readUint32()</code><span><a class="mark" href="#deserializerreaduint32" id="deserializerreaduint32">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_readuint32"></a></h5> 8941cb0ef41Sopenharmony_ci<ul> 8951cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 8961cb0ef41Sopenharmony_ci</ul> 8971cb0ef41Sopenharmony_ci<p>Read a raw 32-bit unsigned integer and return it. 8981cb0ef41Sopenharmony_ciFor use inside of a custom <a href="#deserializer_readhostobject"><code>deserializer._readHostObject()</code></a>.</p> 8991cb0ef41Sopenharmony_ci<h5><code>deserializer.readUint64()</code><span><a class="mark" href="#deserializerreaduint64" id="deserializerreaduint64">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_readuint64"></a></h5> 9001cb0ef41Sopenharmony_ci<ul> 9011cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer[]></a></li> 9021cb0ef41Sopenharmony_ci</ul> 9031cb0ef41Sopenharmony_ci<p>Read a raw 64-bit unsigned integer and return it as an array <code>[hi, lo]</code> 9041cb0ef41Sopenharmony_ciwith two 32-bit unsigned integer entries. 9051cb0ef41Sopenharmony_ciFor use inside of a custom <a href="#deserializer_readhostobject"><code>deserializer._readHostObject()</code></a>.</p> 9061cb0ef41Sopenharmony_ci<h5><code>deserializer.readDouble()</code><span><a class="mark" href="#deserializerreaddouble" id="deserializerreaddouble">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_readdouble"></a></h5> 9071cb0ef41Sopenharmony_ci<ul> 9081cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 9091cb0ef41Sopenharmony_ci</ul> 9101cb0ef41Sopenharmony_ci<p>Read a JS <code>number</code> value. 9111cb0ef41Sopenharmony_ciFor use inside of a custom <a href="#deserializer_readhostobject"><code>deserializer._readHostObject()</code></a>.</p> 9121cb0ef41Sopenharmony_ci<h5><code>deserializer.readRawBytes(length)</code><span><a class="mark" href="#deserializerreadrawbyteslength" id="deserializerreadrawbyteslength">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_readrawbytes_length"></a></h5> 9131cb0ef41Sopenharmony_ci<ul> 9141cb0ef41Sopenharmony_ci<li><code>length</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 9151cb0ef41Sopenharmony_ci<li>Returns: <a href="buffer.html#class-buffer" class="type"><Buffer></a></li> 9161cb0ef41Sopenharmony_ci</ul> 9171cb0ef41Sopenharmony_ci<p>Read raw bytes from the deserializer's internal buffer. The <code>length</code> parameter 9181cb0ef41Sopenharmony_cimust correspond to the length of the buffer that was passed to 9191cb0ef41Sopenharmony_ci<a href="#serializerwriterawbytesbuffer"><code>serializer.writeRawBytes()</code></a>. 9201cb0ef41Sopenharmony_ciFor use inside of a custom <a href="#deserializer_readhostobject"><code>deserializer._readHostObject()</code></a>.</p> 9211cb0ef41Sopenharmony_ci<h5><code>deserializer._readHostObject()</code><span><a class="mark" href="#deserializer_readhostobject" id="deserializer_readhostobject">#</a></span><a aria-hidden="true" class="legacy" id="v8_deserializer_readhostobject"></a></h5> 9221cb0ef41Sopenharmony_ci<p>This method is called to read some kind of host object, i.e. an object that is 9231cb0ef41Sopenharmony_cicreated by native C++ bindings. If it is not possible to deserialize the data, 9241cb0ef41Sopenharmony_cia suitable exception should be thrown.</p> 9251cb0ef41Sopenharmony_ci<p>This method is not present on the <code>Deserializer</code> class itself but can be 9261cb0ef41Sopenharmony_ciprovided by subclasses.</p> 9271cb0ef41Sopenharmony_ci<h4>Class: <code>v8.DefaultSerializer</code><span><a class="mark" href="#class-v8defaultserializer" id="class-v8defaultserializer">#</a></span><a aria-hidden="true" class="legacy" id="v8_class_v8_defaultserializer"></a></h4> 9281cb0ef41Sopenharmony_ci<div class="api_metadata"> 9291cb0ef41Sopenharmony_ci<span>Added in: v8.0.0</span> 9301cb0ef41Sopenharmony_ci</div> 9311cb0ef41Sopenharmony_ci<p>A subclass of <a href="#class-v8serializer"><code>Serializer</code></a> that serializes <code>TypedArray</code> 9321cb0ef41Sopenharmony_ci(in particular <a href="buffer.html"><code>Buffer</code></a>) and <code>DataView</code> objects as host objects, and only 9331cb0ef41Sopenharmony_cistores the part of their underlying <code>ArrayBuffer</code>s that they are referring to.</p> 9341cb0ef41Sopenharmony_ci<h4>Class: <code>v8.DefaultDeserializer</code><span><a class="mark" href="#class-v8defaultdeserializer" id="class-v8defaultdeserializer">#</a></span><a aria-hidden="true" class="legacy" id="v8_class_v8_defaultdeserializer"></a></h4> 9351cb0ef41Sopenharmony_ci<div class="api_metadata"> 9361cb0ef41Sopenharmony_ci<span>Added in: v8.0.0</span> 9371cb0ef41Sopenharmony_ci</div> 9381cb0ef41Sopenharmony_ci<p>A subclass of <a href="#class-v8deserializer"><code>Deserializer</code></a> corresponding to the format written by 9391cb0ef41Sopenharmony_ci<a href="#class-v8defaultserializer"><code>DefaultSerializer</code></a>.</p> 9401cb0ef41Sopenharmony_ci</section><section><h3>Promise hooks<span><a class="mark" href="#promise-hooks" id="promise-hooks">#</a></span><a aria-hidden="true" class="legacy" id="v8_promise_hooks"></a></h3> 9411cb0ef41Sopenharmony_ci<p>The <code>promiseHooks</code> interface can be used to track promise lifecycle events. 9421cb0ef41Sopenharmony_ciTo track <em>all</em> async activity, see <a href="async_hooks.html"><code>async_hooks</code></a> which internally uses this 9431cb0ef41Sopenharmony_cimodule to produce promise lifecycle events in addition to events for other 9441cb0ef41Sopenharmony_ciasync resources. For request context management, see <a href="async_context.html#class-asynclocalstorage"><code>AsyncLocalStorage</code></a>.</p> 9451cb0ef41Sopenharmony_ci<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { promiseHooks } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:v8'</span>; 9461cb0ef41Sopenharmony_ci 9471cb0ef41Sopenharmony_ci<span class="hljs-comment">// There are four lifecycle events produced by promises:</span> 9481cb0ef41Sopenharmony_ci 9491cb0ef41Sopenharmony_ci<span class="hljs-comment">// The `init` event represents the creation of a promise. This could be a</span> 9501cb0ef41Sopenharmony_ci<span class="hljs-comment">// direct creation such as with `new Promise(...)` or a continuation such</span> 9511cb0ef41Sopenharmony_ci<span class="hljs-comment">// as `then()` or `catch()`. It also happens whenever an async function is</span> 9521cb0ef41Sopenharmony_ci<span class="hljs-comment">// called or does an `await`. If a continuation promise is created, the</span> 9531cb0ef41Sopenharmony_ci<span class="hljs-comment">// `parent` will be the promise it is a continuation from.</span> 9541cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">init</span>(<span class="hljs-params">promise, parent</span>) { 9551cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'a promise was created'</span>, { promise, parent }); 9561cb0ef41Sopenharmony_ci} 9571cb0ef41Sopenharmony_ci 9581cb0ef41Sopenharmony_ci<span class="hljs-comment">// The `settled` event happens when a promise receives a resolution or</span> 9591cb0ef41Sopenharmony_ci<span class="hljs-comment">// rejection value. This may happen synchronously such as when using</span> 9601cb0ef41Sopenharmony_ci<span class="hljs-comment">// `Promise.resolve()` on non-promise input.</span> 9611cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">settled</span>(<span class="hljs-params">promise</span>) { 9621cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'a promise resolved or rejected'</span>, { promise }); 9631cb0ef41Sopenharmony_ci} 9641cb0ef41Sopenharmony_ci 9651cb0ef41Sopenharmony_ci<span class="hljs-comment">// The `before` event runs immediately before a `then()` or `catch()` handler</span> 9661cb0ef41Sopenharmony_ci<span class="hljs-comment">// runs or an `await` resumes execution.</span> 9671cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">before</span>(<span class="hljs-params">promise</span>) { 9681cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'a promise is about to call a then handler'</span>, { promise }); 9691cb0ef41Sopenharmony_ci} 9701cb0ef41Sopenharmony_ci 9711cb0ef41Sopenharmony_ci<span class="hljs-comment">// The `after` event runs immediately after a `then()` handler runs or when</span> 9721cb0ef41Sopenharmony_ci<span class="hljs-comment">// an `await` begins after resuming from another.</span> 9731cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">after</span>(<span class="hljs-params">promise</span>) { 9741cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'a promise is done calling a then handler'</span>, { promise }); 9751cb0ef41Sopenharmony_ci} 9761cb0ef41Sopenharmony_ci 9771cb0ef41Sopenharmony_ci<span class="hljs-comment">// Lifecycle hooks may be started and stopped individually</span> 9781cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stopWatchingInits = promiseHooks.<span class="hljs-title function_">onInit</span>(init); 9791cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stopWatchingSettleds = promiseHooks.<span class="hljs-title function_">onSettled</span>(settled); 9801cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stopWatchingBefores = promiseHooks.<span class="hljs-title function_">onBefore</span>(before); 9811cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stopWatchingAfters = promiseHooks.<span class="hljs-title function_">onAfter</span>(after); 9821cb0ef41Sopenharmony_ci 9831cb0ef41Sopenharmony_ci<span class="hljs-comment">// Or they may be started and stopped in groups</span> 9841cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stopHookSet = promiseHooks.<span class="hljs-title function_">createHook</span>({ 9851cb0ef41Sopenharmony_ci init, 9861cb0ef41Sopenharmony_ci settled, 9871cb0ef41Sopenharmony_ci before, 9881cb0ef41Sopenharmony_ci after, 9891cb0ef41Sopenharmony_ci}); 9901cb0ef41Sopenharmony_ci 9911cb0ef41Sopenharmony_ci<span class="hljs-comment">// To stop a hook, call the function returned at its creation.</span> 9921cb0ef41Sopenharmony_ci<span class="hljs-title function_">stopWatchingInits</span>(); 9931cb0ef41Sopenharmony_ci<span class="hljs-title function_">stopWatchingSettleds</span>(); 9941cb0ef41Sopenharmony_ci<span class="hljs-title function_">stopWatchingBefores</span>(); 9951cb0ef41Sopenharmony_ci<span class="hljs-title function_">stopWatchingAfters</span>(); 9961cb0ef41Sopenharmony_ci<span class="hljs-title function_">stopHookSet</span>();</code> <button class="copy-button">copy</button></pre> 9971cb0ef41Sopenharmony_ci<h4><code>promiseHooks.onInit(init)</code><span><a class="mark" href="#promisehooksoninitinit" id="promisehooksoninitinit">#</a></span><a aria-hidden="true" class="legacy" id="v8_promisehooks_oninit_init"></a></h4> 9981cb0ef41Sopenharmony_ci<div class="api_metadata"> 9991cb0ef41Sopenharmony_ci<span>Added in: v17.1.0, v16.14.0</span> 10001cb0ef41Sopenharmony_ci</div> 10011cb0ef41Sopenharmony_ci<ul> 10021cb0ef41Sopenharmony_ci<li><code>init</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#initpromise-parent"><code>init</code> callback</a> to call when a promise is created.</li> 10031cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Call to stop the hook.</li> 10041cb0ef41Sopenharmony_ci</ul> 10051cb0ef41Sopenharmony_ci<p><strong>The <code>init</code> hook must be a plain function. Providing an async function will 10061cb0ef41Sopenharmony_cithrow as it would produce an infinite microtask loop.</strong></p> 10071cb0ef41Sopenharmony_ci 10081cb0ef41Sopenharmony_ci<pre class="with-44-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { promiseHooks } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:v8'</span>; 10091cb0ef41Sopenharmony_ci 10101cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stop = promiseHooks.<span class="hljs-title function_">onInit</span>(<span class="hljs-function">(<span class="hljs-params">promise, parent</span>) =></span> {});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { promiseHooks } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 10111cb0ef41Sopenharmony_ci 10121cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stop = promiseHooks.<span class="hljs-title function_">onInit</span>(<span class="hljs-function">(<span class="hljs-params">promise, parent</span>) =></span> {});</code><button class="copy-button">copy</button></pre> 10131cb0ef41Sopenharmony_ci<h4><code>promiseHooks.onSettled(settled)</code><span><a class="mark" href="#promisehooksonsettledsettled" id="promisehooksonsettledsettled">#</a></span><a aria-hidden="true" class="legacy" id="v8_promisehooks_onsettled_settled"></a></h4> 10141cb0ef41Sopenharmony_ci<div class="api_metadata"> 10151cb0ef41Sopenharmony_ci<span>Added in: v17.1.0, v16.14.0</span> 10161cb0ef41Sopenharmony_ci</div> 10171cb0ef41Sopenharmony_ci<ul> 10181cb0ef41Sopenharmony_ci<li><code>settled</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#settledpromise"><code>settled</code> callback</a> to call when a promise 10191cb0ef41Sopenharmony_ciis resolved or rejected.</li> 10201cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Call to stop the hook.</li> 10211cb0ef41Sopenharmony_ci</ul> 10221cb0ef41Sopenharmony_ci<p><strong>The <code>settled</code> hook must be a plain function. Providing an async function will 10231cb0ef41Sopenharmony_cithrow as it would produce an infinite microtask loop.</strong></p> 10241cb0ef41Sopenharmony_ci 10251cb0ef41Sopenharmony_ci<pre class="with-44-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { promiseHooks } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:v8'</span>; 10261cb0ef41Sopenharmony_ci 10271cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stop = promiseHooks.<span class="hljs-title function_">onSettled</span>(<span class="hljs-function">(<span class="hljs-params">promise</span>) =></span> {});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { promiseHooks } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 10281cb0ef41Sopenharmony_ci 10291cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stop = promiseHooks.<span class="hljs-title function_">onSettled</span>(<span class="hljs-function">(<span class="hljs-params">promise</span>) =></span> {});</code><button class="copy-button">copy</button></pre> 10301cb0ef41Sopenharmony_ci<h4><code>promiseHooks.onBefore(before)</code><span><a class="mark" href="#promisehooksonbeforebefore" id="promisehooksonbeforebefore">#</a></span><a aria-hidden="true" class="legacy" id="v8_promisehooks_onbefore_before"></a></h4> 10311cb0ef41Sopenharmony_ci<div class="api_metadata"> 10321cb0ef41Sopenharmony_ci<span>Added in: v17.1.0, v16.14.0</span> 10331cb0ef41Sopenharmony_ci</div> 10341cb0ef41Sopenharmony_ci<ul> 10351cb0ef41Sopenharmony_ci<li><code>before</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#beforepromise"><code>before</code> callback</a> to call before a promise 10361cb0ef41Sopenharmony_cicontinuation executes.</li> 10371cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Call to stop the hook.</li> 10381cb0ef41Sopenharmony_ci</ul> 10391cb0ef41Sopenharmony_ci<p><strong>The <code>before</code> hook must be a plain function. Providing an async function will 10401cb0ef41Sopenharmony_cithrow as it would produce an infinite microtask loop.</strong></p> 10411cb0ef41Sopenharmony_ci 10421cb0ef41Sopenharmony_ci<pre class="with-44-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { promiseHooks } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:v8'</span>; 10431cb0ef41Sopenharmony_ci 10441cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stop = promiseHooks.<span class="hljs-title function_">onBefore</span>(<span class="hljs-function">(<span class="hljs-params">promise</span>) =></span> {});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { promiseHooks } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 10451cb0ef41Sopenharmony_ci 10461cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stop = promiseHooks.<span class="hljs-title function_">onBefore</span>(<span class="hljs-function">(<span class="hljs-params">promise</span>) =></span> {});</code><button class="copy-button">copy</button></pre> 10471cb0ef41Sopenharmony_ci<h4><code>promiseHooks.onAfter(after)</code><span><a class="mark" href="#promisehooksonafterafter" id="promisehooksonafterafter">#</a></span><a aria-hidden="true" class="legacy" id="v8_promisehooks_onafter_after"></a></h4> 10481cb0ef41Sopenharmony_ci<div class="api_metadata"> 10491cb0ef41Sopenharmony_ci<span>Added in: v17.1.0, v16.14.0</span> 10501cb0ef41Sopenharmony_ci</div> 10511cb0ef41Sopenharmony_ci<ul> 10521cb0ef41Sopenharmony_ci<li><code>after</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#afterpromise"><code>after</code> callback</a> to call after a promise 10531cb0ef41Sopenharmony_cicontinuation executes.</li> 10541cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Call to stop the hook.</li> 10551cb0ef41Sopenharmony_ci</ul> 10561cb0ef41Sopenharmony_ci<p><strong>The <code>after</code> hook must be a plain function. Providing an async function will 10571cb0ef41Sopenharmony_cithrow as it would produce an infinite microtask loop.</strong></p> 10581cb0ef41Sopenharmony_ci 10591cb0ef41Sopenharmony_ci<pre class="with-44-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { promiseHooks } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:v8'</span>; 10601cb0ef41Sopenharmony_ci 10611cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stop = promiseHooks.<span class="hljs-title function_">onAfter</span>(<span class="hljs-function">(<span class="hljs-params">promise</span>) =></span> {});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { promiseHooks } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 10621cb0ef41Sopenharmony_ci 10631cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stop = promiseHooks.<span class="hljs-title function_">onAfter</span>(<span class="hljs-function">(<span class="hljs-params">promise</span>) =></span> {});</code><button class="copy-button">copy</button></pre> 10641cb0ef41Sopenharmony_ci<h4><code>promiseHooks.createHook(callbacks)</code><span><a class="mark" href="#promisehookscreatehookcallbacks" id="promisehookscreatehookcallbacks">#</a></span><a aria-hidden="true" class="legacy" id="v8_promisehooks_createhook_callbacks"></a></h4> 10651cb0ef41Sopenharmony_ci<div class="api_metadata"> 10661cb0ef41Sopenharmony_ci<span>Added in: v17.1.0, v16.14.0</span> 10671cb0ef41Sopenharmony_ci</div> 10681cb0ef41Sopenharmony_ci<ul> 10691cb0ef41Sopenharmony_ci<li><code>callbacks</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The <a href="#hook-callbacks">Hook Callbacks</a> to register 10701cb0ef41Sopenharmony_ci<ul> 10711cb0ef41Sopenharmony_ci<li><code>init</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#initpromise-parent"><code>init</code> callback</a>.</li> 10721cb0ef41Sopenharmony_ci<li><code>before</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#beforepromise"><code>before</code> callback</a>.</li> 10731cb0ef41Sopenharmony_ci<li><code>after</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#afterpromise"><code>after</code> callback</a>.</li> 10741cb0ef41Sopenharmony_ci<li><code>settled</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#settledpromise"><code>settled</code> callback</a>.</li> 10751cb0ef41Sopenharmony_ci</ul> 10761cb0ef41Sopenharmony_ci</li> 10771cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Used for disabling hooks</li> 10781cb0ef41Sopenharmony_ci</ul> 10791cb0ef41Sopenharmony_ci<p><strong>The hook callbacks must be plain functions. Providing async functions will 10801cb0ef41Sopenharmony_cithrow as it would produce an infinite microtask loop.</strong></p> 10811cb0ef41Sopenharmony_ci<p>Registers functions to be called for different lifetime events of each promise.</p> 10821cb0ef41Sopenharmony_ci<p>The callbacks <code>init()</code>/<code>before()</code>/<code>after()</code>/<code>settled()</code> are called for the 10831cb0ef41Sopenharmony_cirespective events during a promise's lifetime.</p> 10841cb0ef41Sopenharmony_ci<p>All callbacks are optional. For example, if only promise creation needs to 10851cb0ef41Sopenharmony_cibe tracked, then only the <code>init</code> callback needs to be passed. The 10861cb0ef41Sopenharmony_cispecifics of all functions that can be passed to <code>callbacks</code> is in the 10871cb0ef41Sopenharmony_ci<a href="#hook-callbacks">Hook Callbacks</a> section.</p> 10881cb0ef41Sopenharmony_ci 10891cb0ef41Sopenharmony_ci<pre class="with-44-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { promiseHooks } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:v8'</span>; 10901cb0ef41Sopenharmony_ci 10911cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stopAll = promiseHooks.<span class="hljs-title function_">createHook</span>({ 10921cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">promise, parent</span>) {}, 10931cb0ef41Sopenharmony_ci});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { promiseHooks } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 10941cb0ef41Sopenharmony_ci 10951cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> stopAll = promiseHooks.<span class="hljs-title function_">createHook</span>({ 10961cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">promise, parent</span>) {}, 10971cb0ef41Sopenharmony_ci});</code><button class="copy-button">copy</button></pre> 10981cb0ef41Sopenharmony_ci<h4>Hook callbacks<span><a class="mark" href="#hook-callbacks" id="hook-callbacks">#</a></span><a aria-hidden="true" class="legacy" id="v8_hook_callbacks"></a></h4> 10991cb0ef41Sopenharmony_ci<p>Key events in the lifetime of a promise have been categorized into four areas: 11001cb0ef41Sopenharmony_cicreation of a promise, before/after a continuation handler is called or around 11011cb0ef41Sopenharmony_cian await, and when the promise resolves or rejects.</p> 11021cb0ef41Sopenharmony_ci<p>While these hooks are similar to those of <a href="async_hooks.html"><code>async_hooks</code></a> they lack a 11031cb0ef41Sopenharmony_ci<code>destroy</code> hook. Other types of async resources typically represent sockets or 11041cb0ef41Sopenharmony_cifile descriptors which have a distinct "closed" state to express the <code>destroy</code> 11051cb0ef41Sopenharmony_cilifecycle event while promises remain usable for as long as code can still 11061cb0ef41Sopenharmony_cireach them. Garbage collection tracking is used to make promises fit into the 11071cb0ef41Sopenharmony_ci<code>async_hooks</code> event model, however this tracking is very expensive and they may 11081cb0ef41Sopenharmony_cinot necessarily ever even be garbage collected.</p> 11091cb0ef41Sopenharmony_ci<p>Because promises are asynchronous resources whose lifecycle is tracked 11101cb0ef41Sopenharmony_civia the promise hooks mechanism, the <code>init()</code>, <code>before()</code>, <code>after()</code>, and 11111cb0ef41Sopenharmony_ci<code>settled()</code> callbacks <em>must not</em> be async functions as they create more 11121cb0ef41Sopenharmony_cipromises which would produce an infinite loop.</p> 11131cb0ef41Sopenharmony_ci<p>While this API is used to feed promise events into <a href="async_hooks.html"><code>async_hooks</code></a>, the 11141cb0ef41Sopenharmony_ciordering between the two is undefined. Both APIs are multi-tenant 11151cb0ef41Sopenharmony_ciand therefore could produce events in any order relative to each other.</p> 11161cb0ef41Sopenharmony_ci<h5><code>init(promise, parent)</code><span><a class="mark" href="#initpromise-parent" id="initpromise-parent">#</a></span><a aria-hidden="true" class="legacy" id="v8_init_promise_parent"></a></h5> 11171cb0ef41Sopenharmony_ci<ul> 11181cb0ef41Sopenharmony_ci<li><code>promise</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> The promise being created.</li> 11191cb0ef41Sopenharmony_ci<li><code>parent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> The promise continued from, if applicable.</li> 11201cb0ef41Sopenharmony_ci</ul> 11211cb0ef41Sopenharmony_ci<p>Called when a promise is constructed. This <em>does not</em> mean that corresponding 11221cb0ef41Sopenharmony_ci<code>before</code>/<code>after</code> events will occur, only that the possibility exists. This will 11231cb0ef41Sopenharmony_cihappen if a promise is created without ever getting a continuation.</p> 11241cb0ef41Sopenharmony_ci<h5><code>before(promise)</code><span><a class="mark" href="#beforepromise" id="beforepromise">#</a></span><a aria-hidden="true" class="legacy" id="v8_before_promise"></a></h5> 11251cb0ef41Sopenharmony_ci<ul> 11261cb0ef41Sopenharmony_ci<li><code>promise</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li> 11271cb0ef41Sopenharmony_ci</ul> 11281cb0ef41Sopenharmony_ci<p>Called before a promise continuation executes. This can be in the form of 11291cb0ef41Sopenharmony_ci<code>then()</code>, <code>catch()</code>, or <code>finally()</code> handlers or an <code>await</code> resuming.</p> 11301cb0ef41Sopenharmony_ci<p>The <code>before</code> callback will be called 0 to N times. The <code>before</code> callback 11311cb0ef41Sopenharmony_ciwill typically be called 0 times if no continuation was ever made for the 11321cb0ef41Sopenharmony_cipromise. The <code>before</code> callback may be called many times in the case where 11331cb0ef41Sopenharmony_cimany continuations have been made from the same promise.</p> 11341cb0ef41Sopenharmony_ci<h5><code>after(promise)</code><span><a class="mark" href="#afterpromise" id="afterpromise">#</a></span><a aria-hidden="true" class="legacy" id="v8_after_promise"></a></h5> 11351cb0ef41Sopenharmony_ci<ul> 11361cb0ef41Sopenharmony_ci<li><code>promise</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li> 11371cb0ef41Sopenharmony_ci</ul> 11381cb0ef41Sopenharmony_ci<p>Called immediately after a promise continuation executes. This may be after a 11391cb0ef41Sopenharmony_ci<code>then()</code>, <code>catch()</code>, or <code>finally()</code> handler or before an <code>await</code> after another 11401cb0ef41Sopenharmony_ci<code>await</code>.</p> 11411cb0ef41Sopenharmony_ci<h5><code>settled(promise)</code><span><a class="mark" href="#settledpromise" id="settledpromise">#</a></span><a aria-hidden="true" class="legacy" id="v8_settled_promise"></a></h5> 11421cb0ef41Sopenharmony_ci<ul> 11431cb0ef41Sopenharmony_ci<li><code>promise</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li> 11441cb0ef41Sopenharmony_ci</ul> 11451cb0ef41Sopenharmony_ci<p>Called when the promise receives a resolution or rejection value. This may 11461cb0ef41Sopenharmony_cioccur synchronously in the case of <code>Promise.resolve()</code> or <code>Promise.reject()</code>.</p> 11471cb0ef41Sopenharmony_ci</section><section><h3>Startup Snapshot API<span><a class="mark" href="#startup-snapshot-api" id="startup-snapshot-api">#</a></span><a aria-hidden="true" class="legacy" id="v8_startup_snapshot_api"></a></h3> 11481cb0ef41Sopenharmony_ci<div class="api_metadata"> 11491cb0ef41Sopenharmony_ci<span>Added in: v18.6.0</span> 11501cb0ef41Sopenharmony_ci</div> 11511cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 11521cb0ef41Sopenharmony_ci<p>The <code>v8.startupSnapshot</code> interface can be used to add serialization and 11531cb0ef41Sopenharmony_cideserialization hooks for custom startup snapshots.</p> 11541cb0ef41Sopenharmony_ci<pre><code class="language-console"><span class="hljs-meta prompt_">$ </span><span class="language-bash">node --snapshot-blob snapshot.blob --build-snapshot entry.js</span> 11551cb0ef41Sopenharmony_ci<span class="hljs-meta prompt_"># </span><span class="language-bash">This launches a process with the snapshot</span> 11561cb0ef41Sopenharmony_ci<span class="hljs-meta prompt_">$ </span><span class="language-bash">node --snapshot-blob snapshot.blob</span></code> <button class="copy-button">copy</button></pre> 11571cb0ef41Sopenharmony_ci<p>In the example above, <code>entry.js</code> can use methods from the <code>v8.startupSnapshot</code> 11581cb0ef41Sopenharmony_ciinterface to specify how to save information for custom objects in the snapshot 11591cb0ef41Sopenharmony_ciduring serialization and how the information can be used to synchronize these 11601cb0ef41Sopenharmony_ciobjects during deserialization of the snapshot. For example, if the <code>entry.js</code> 11611cb0ef41Sopenharmony_cicontains the following script:</p> 11621cb0ef41Sopenharmony_ci<pre><code class="language-js cjs"><span class="hljs-meta">'use strict'</span>; 11631cb0ef41Sopenharmony_ci 11641cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); 11651cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> zlib = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:zlib'</span>); 11661cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> path = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:path'</span>); 11671cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>); 11681cb0ef41Sopenharmony_ci 11691cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> v8 = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:v8'</span>); 11701cb0ef41Sopenharmony_ci 11711cb0ef41Sopenharmony_ci<span class="hljs-keyword">class</span> <span class="hljs-title class_">BookShelf</span> { 11721cb0ef41Sopenharmony_ci storage = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Map</span>(); 11731cb0ef41Sopenharmony_ci 11741cb0ef41Sopenharmony_ci <span class="hljs-comment">// Reading a series of files from directory and store them into storage.</span> 11751cb0ef41Sopenharmony_ci <span class="hljs-title function_">constructor</span>(<span class="hljs-params">directory, books</span>) { 11761cb0ef41Sopenharmony_ci <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> book <span class="hljs-keyword">of</span> books) { 11771cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">storage</span>.<span class="hljs-title function_">set</span>(book, fs.<span class="hljs-title function_">readFileSync</span>(path.<span class="hljs-title function_">join</span>(directory, book))); 11781cb0ef41Sopenharmony_ci } 11791cb0ef41Sopenharmony_ci } 11801cb0ef41Sopenharmony_ci 11811cb0ef41Sopenharmony_ci <span class="hljs-keyword">static</span> <span class="hljs-title function_">compressAll</span>(<span class="hljs-params">shelf</span>) { 11821cb0ef41Sopenharmony_ci <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> [ book, content ] <span class="hljs-keyword">of</span> shelf.<span class="hljs-property">storage</span>) { 11831cb0ef41Sopenharmony_ci shelf.<span class="hljs-property">storage</span>.<span class="hljs-title function_">set</span>(book, zlib.<span class="hljs-title function_">gzipSync</span>(content)); 11841cb0ef41Sopenharmony_ci } 11851cb0ef41Sopenharmony_ci } 11861cb0ef41Sopenharmony_ci 11871cb0ef41Sopenharmony_ci <span class="hljs-keyword">static</span> <span class="hljs-title function_">decompressAll</span>(<span class="hljs-params">shelf</span>) { 11881cb0ef41Sopenharmony_ci <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> [ book, content ] <span class="hljs-keyword">of</span> shelf.<span class="hljs-property">storage</span>) { 11891cb0ef41Sopenharmony_ci shelf.<span class="hljs-property">storage</span>.<span class="hljs-title function_">set</span>(book, zlib.<span class="hljs-title function_">gunzipSync</span>(content)); 11901cb0ef41Sopenharmony_ci } 11911cb0ef41Sopenharmony_ci } 11921cb0ef41Sopenharmony_ci} 11931cb0ef41Sopenharmony_ci 11941cb0ef41Sopenharmony_ci<span class="hljs-comment">// __dirname here is where the snapshot script is placed</span> 11951cb0ef41Sopenharmony_ci<span class="hljs-comment">// during snapshot building time.</span> 11961cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> shelf = <span class="hljs-keyword">new</span> <span class="hljs-title class_">BookShelf</span>(__dirname, [ 11971cb0ef41Sopenharmony_ci <span class="hljs-string">'book1.en_US.txt'</span>, 11981cb0ef41Sopenharmony_ci <span class="hljs-string">'book1.es_ES.txt'</span>, 11991cb0ef41Sopenharmony_ci <span class="hljs-string">'book2.zh_CN.txt'</span>, 12001cb0ef41Sopenharmony_ci]); 12011cb0ef41Sopenharmony_ci 12021cb0ef41Sopenharmony_ci<span class="hljs-title function_">assert</span>(v8.<span class="hljs-property">startupSnapshot</span>.<span class="hljs-title function_">isBuildingSnapshot</span>()); 12031cb0ef41Sopenharmony_ci<span class="hljs-comment">// On snapshot serialization, compress the books to reduce size.</span> 12041cb0ef41Sopenharmony_civ8.<span class="hljs-property">startupSnapshot</span>.<span class="hljs-title function_">addSerializeCallback</span>(<span class="hljs-title class_">BookShelf</span>.<span class="hljs-property">compressAll</span>, shelf); 12051cb0ef41Sopenharmony_ci<span class="hljs-comment">// On snapshot deserialization, decompress the books.</span> 12061cb0ef41Sopenharmony_civ8.<span class="hljs-property">startupSnapshot</span>.<span class="hljs-title function_">addDeserializeCallback</span>(<span class="hljs-title class_">BookShelf</span>.<span class="hljs-property">decompressAll</span>, shelf); 12071cb0ef41Sopenharmony_civ8.<span class="hljs-property">startupSnapshot</span>.<span class="hljs-title function_">setDeserializeMainFunction</span>(<span class="hljs-function">(<span class="hljs-params">shelf</span>) =></span> { 12081cb0ef41Sopenharmony_ci <span class="hljs-comment">// process.env and process.argv are refreshed during snapshot</span> 12091cb0ef41Sopenharmony_ci <span class="hljs-comment">// deserialization.</span> 12101cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> lang = process.<span class="hljs-property">env</span>.<span class="hljs-property">BOOK_LANG</span> || <span class="hljs-string">'en_US'</span>; 12111cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> book = process.<span class="hljs-property">argv</span>[<span class="hljs-number">1</span>]; 12121cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> name = <span class="hljs-string">`<span class="hljs-subst">${book}</span>.<span class="hljs-subst">${lang}</span>.txt`</span>; 12131cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(shelf.<span class="hljs-property">storage</span>.<span class="hljs-title function_">get</span>(name)); 12141cb0ef41Sopenharmony_ci}, shelf);</code> <button class="copy-button">copy</button></pre> 12151cb0ef41Sopenharmony_ci<p>The resulted binary will get print the data deserialized from the snapshot 12161cb0ef41Sopenharmony_ciduring start up, using the refreshed <code>process.env</code> and <code>process.argv</code> of 12171cb0ef41Sopenharmony_cithe launched process:</p> 12181cb0ef41Sopenharmony_ci<pre><code class="language-console"><span class="hljs-meta prompt_">$ </span><span class="language-bash">BOOK_LANG=es_ES node --snapshot-blob snapshot.blob book1</span> 12191cb0ef41Sopenharmony_ci<span class="hljs-meta prompt_"># </span><span class="language-bash">Prints content of book1.es_ES.txt deserialized from the snapshot.</span></code> <button class="copy-button">copy</button></pre> 12201cb0ef41Sopenharmony_ci<p>Currently the application deserialized from a user-land snapshot cannot 12211cb0ef41Sopenharmony_cibe snapshotted again, so these APIs are only available to applications 12221cb0ef41Sopenharmony_cithat are not deserialized from a user-land snapshot.</p> 12231cb0ef41Sopenharmony_ci<h4><code>v8.startupSnapshot.addSerializeCallback(callback[, data])</code><span><a class="mark" href="#v8startupsnapshotaddserializecallbackcallback-data" id="v8startupsnapshotaddserializecallbackcallback-data">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_startupsnapshot_addserializecallback_callback_data"></a></h4> 12241cb0ef41Sopenharmony_ci<div class="api_metadata"> 12251cb0ef41Sopenharmony_ci<span>Added in: v18.6.0</span> 12261cb0ef41Sopenharmony_ci</div> 12271cb0ef41Sopenharmony_ci<ul> 12281cb0ef41Sopenharmony_ci<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Callback to be invoked before serialization.</li> 12291cb0ef41Sopenharmony_ci<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Optional data that will be passed to the <code>callback</code> when it 12301cb0ef41Sopenharmony_cigets called.</li> 12311cb0ef41Sopenharmony_ci</ul> 12321cb0ef41Sopenharmony_ci<p>Add a callback that will be called when the Node.js instance is about to 12331cb0ef41Sopenharmony_ciget serialized into a snapshot and exit. This can be used to release 12341cb0ef41Sopenharmony_ciresources that should not or cannot be serialized or to convert user data 12351cb0ef41Sopenharmony_ciinto a form more suitable for serialization.</p> 12361cb0ef41Sopenharmony_ci<h4><code>v8.startupSnapshot.addDeserializeCallback(callback[, data])</code><span><a class="mark" href="#v8startupsnapshotadddeserializecallbackcallback-data" id="v8startupsnapshotadddeserializecallbackcallback-data">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_startupsnapshot_adddeserializecallback_callback_data"></a></h4> 12371cb0ef41Sopenharmony_ci<div class="api_metadata"> 12381cb0ef41Sopenharmony_ci<span>Added in: v18.6.0</span> 12391cb0ef41Sopenharmony_ci</div> 12401cb0ef41Sopenharmony_ci<ul> 12411cb0ef41Sopenharmony_ci<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Callback to be invoked after the snapshot is 12421cb0ef41Sopenharmony_cideserialized.</li> 12431cb0ef41Sopenharmony_ci<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Optional data that will be passed to the <code>callback</code> when it 12441cb0ef41Sopenharmony_cigets called.</li> 12451cb0ef41Sopenharmony_ci</ul> 12461cb0ef41Sopenharmony_ci<p>Add a callback that will be called when the Node.js instance is deserialized 12471cb0ef41Sopenharmony_cifrom a snapshot. The <code>callback</code> and the <code>data</code> (if provided) will be 12481cb0ef41Sopenharmony_ciserialized into the snapshot, they can be used to re-initialize the state 12491cb0ef41Sopenharmony_ciof the application or to re-acquire resources that the application needs 12501cb0ef41Sopenharmony_ciwhen the application is restarted from the snapshot.</p> 12511cb0ef41Sopenharmony_ci<h4><code>v8.startupSnapshot.setDeserializeMainFunction(callback[, data])</code><span><a class="mark" href="#v8startupsnapshotsetdeserializemainfunctioncallback-data" id="v8startupsnapshotsetdeserializemainfunctioncallback-data">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_startupsnapshot_setdeserializemainfunction_callback_data"></a></h4> 12521cb0ef41Sopenharmony_ci<div class="api_metadata"> 12531cb0ef41Sopenharmony_ci<span>Added in: v18.6.0</span> 12541cb0ef41Sopenharmony_ci</div> 12551cb0ef41Sopenharmony_ci<ul> 12561cb0ef41Sopenharmony_ci<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Callback to be invoked as the entry point after the 12571cb0ef41Sopenharmony_cisnapshot is deserialized.</li> 12581cb0ef41Sopenharmony_ci<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Optional data that will be passed to the <code>callback</code> when it 12591cb0ef41Sopenharmony_cigets called.</li> 12601cb0ef41Sopenharmony_ci</ul> 12611cb0ef41Sopenharmony_ci<p>This sets the entry point of the Node.js application when it is deserialized 12621cb0ef41Sopenharmony_cifrom a snapshot. This can be called only once in the snapshot building 12631cb0ef41Sopenharmony_ciscript. If called, the deserialized application no longer needs an additional 12641cb0ef41Sopenharmony_cientry point script to start up and will simply invoke the callback along with 12651cb0ef41Sopenharmony_cithe deserialized data (if provided), otherwise an entry point script still 12661cb0ef41Sopenharmony_cineeds to be provided to the deserialized application.</p> 12671cb0ef41Sopenharmony_ci<h4><code>v8.startupSnapshot.isBuildingSnapshot()</code><span><a class="mark" href="#v8startupsnapshotisbuildingsnapshot" id="v8startupsnapshotisbuildingsnapshot">#</a></span><a aria-hidden="true" class="legacy" id="v8_v8_startupsnapshot_isbuildingsnapshot"></a></h4> 12681cb0ef41Sopenharmony_ci<div class="api_metadata"> 12691cb0ef41Sopenharmony_ci<span>Added in: v18.6.0</span> 12701cb0ef41Sopenharmony_ci</div> 12711cb0ef41Sopenharmony_ci<ul> 12721cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 12731cb0ef41Sopenharmony_ci</ul> 12741cb0ef41Sopenharmony_ci<p>Returns true if the Node.js instance is run to build a snapshot.</p> 12751cb0ef41Sopenharmony_ci</section><section><h3>Class: <code>v8.GCProfiler</code><span><a class="mark" href="#class-v8gcprofiler" id="class-v8gcprofiler">#</a></span><a aria-hidden="true" class="legacy" id="v8_class_v8_gcprofiler"></a></h3> 12761cb0ef41Sopenharmony_ci<div class="api_metadata"> 12771cb0ef41Sopenharmony_ci<span>Added in: v18.15.0</span> 12781cb0ef41Sopenharmony_ci</div> 12791cb0ef41Sopenharmony_ci<p>This API collects GC data in current thread.</p> 12801cb0ef41Sopenharmony_ci<h4><code>new v8.GCProfiler()</code><span><a class="mark" href="#new-v8gcprofiler" id="new-v8gcprofiler">#</a></span><a aria-hidden="true" class="legacy" id="v8_new_v8_gcprofiler"></a></h4> 12811cb0ef41Sopenharmony_ci<div class="api_metadata"> 12821cb0ef41Sopenharmony_ci<span>Added in: v18.15.0</span> 12831cb0ef41Sopenharmony_ci</div> 12841cb0ef41Sopenharmony_ci<p>Create a new instance of the <code>v8.GCProfiler</code> class.</p> 12851cb0ef41Sopenharmony_ci<h4><code>profiler.start()</code><span><a class="mark" href="#profilerstart" id="profilerstart">#</a></span><a aria-hidden="true" class="legacy" id="v8_profiler_start"></a></h4> 12861cb0ef41Sopenharmony_ci<div class="api_metadata"> 12871cb0ef41Sopenharmony_ci<span>Added in: v18.15.0</span> 12881cb0ef41Sopenharmony_ci</div> 12891cb0ef41Sopenharmony_ci<p>Start collecting GC data.</p> 12901cb0ef41Sopenharmony_ci<h4><code>profiler.stop()</code><span><a class="mark" href="#profilerstop" id="profilerstop">#</a></span><a aria-hidden="true" class="legacy" id="v8_profiler_stop"></a></h4> 12911cb0ef41Sopenharmony_ci<div class="api_metadata"> 12921cb0ef41Sopenharmony_ci<span>Added in: v18.15.0</span> 12931cb0ef41Sopenharmony_ci</div> 12941cb0ef41Sopenharmony_ci<p>Stop collecting GC data and return an object.The content of object 12951cb0ef41Sopenharmony_ciis as follows.</p> 12961cb0ef41Sopenharmony_ci<pre><code class="language-json"><span class="hljs-punctuation">{</span> 12971cb0ef41Sopenharmony_ci <span class="hljs-attr">"version"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1</span><span class="hljs-punctuation">,</span> 12981cb0ef41Sopenharmony_ci <span class="hljs-attr">"startTime"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1674059033862</span><span class="hljs-punctuation">,</span> 12991cb0ef41Sopenharmony_ci <span class="hljs-attr">"statistics"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">[</span> 13001cb0ef41Sopenharmony_ci <span class="hljs-punctuation">{</span> 13011cb0ef41Sopenharmony_ci <span class="hljs-attr">"gcType"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"Scavenge"</span><span class="hljs-punctuation">,</span> 13021cb0ef41Sopenharmony_ci <span class="hljs-attr">"beforeGC"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 13031cb0ef41Sopenharmony_ci <span class="hljs-attr">"heapStatistics"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 13041cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalHeapSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">5005312</span><span class="hljs-punctuation">,</span> 13051cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalHeapSizeExecutable"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">524288</span><span class="hljs-punctuation">,</span> 13061cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalPhysicalSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">5226496</span><span class="hljs-punctuation">,</span> 13071cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalAvailableSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">4341325216</span><span class="hljs-punctuation">,</span> 13081cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalGlobalHandlesSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">8192</span><span class="hljs-punctuation">,</span> 13091cb0ef41Sopenharmony_ci <span class="hljs-attr">"usedGlobalHandlesSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">2112</span><span class="hljs-punctuation">,</span> 13101cb0ef41Sopenharmony_ci <span class="hljs-attr">"usedHeapSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">4883840</span><span class="hljs-punctuation">,</span> 13111cb0ef41Sopenharmony_ci <span class="hljs-attr">"heapSizeLimit"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">4345298944</span><span class="hljs-punctuation">,</span> 13121cb0ef41Sopenharmony_ci <span class="hljs-attr">"mallocedMemory"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">254128</span><span class="hljs-punctuation">,</span> 13131cb0ef41Sopenharmony_ci <span class="hljs-attr">"externalMemory"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">225138</span><span class="hljs-punctuation">,</span> 13141cb0ef41Sopenharmony_ci <span class="hljs-attr">"peakMallocedMemory"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">181760</span> 13151cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 13161cb0ef41Sopenharmony_ci <span class="hljs-attr">"heapSpaceStatistics"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">[</span> 13171cb0ef41Sopenharmony_ci <span class="hljs-punctuation">{</span> 13181cb0ef41Sopenharmony_ci <span class="hljs-attr">"spaceName"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"read_only_space"</span><span class="hljs-punctuation">,</span> 13191cb0ef41Sopenharmony_ci <span class="hljs-attr">"spaceSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 13201cb0ef41Sopenharmony_ci <span class="hljs-attr">"spaceUsedSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 13211cb0ef41Sopenharmony_ci <span class="hljs-attr">"spaceAvailableSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 13221cb0ef41Sopenharmony_ci <span class="hljs-attr">"physicalSpaceSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span> 13231cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span> 13241cb0ef41Sopenharmony_ci <span class="hljs-punctuation">]</span> 13251cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 13261cb0ef41Sopenharmony_ci <span class="hljs-attr">"cost"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1574.14</span><span class="hljs-punctuation">,</span> 13271cb0ef41Sopenharmony_ci <span class="hljs-attr">"afterGC"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 13281cb0ef41Sopenharmony_ci <span class="hljs-attr">"heapStatistics"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 13291cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalHeapSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">6053888</span><span class="hljs-punctuation">,</span> 13301cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalHeapSizeExecutable"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">524288</span><span class="hljs-punctuation">,</span> 13311cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalPhysicalSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">5500928</span><span class="hljs-punctuation">,</span> 13321cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalAvailableSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">4341101384</span><span class="hljs-punctuation">,</span> 13331cb0ef41Sopenharmony_ci <span class="hljs-attr">"totalGlobalHandlesSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">8192</span><span class="hljs-punctuation">,</span> 13341cb0ef41Sopenharmony_ci <span class="hljs-attr">"usedGlobalHandlesSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">2112</span><span class="hljs-punctuation">,</span> 13351cb0ef41Sopenharmony_ci <span class="hljs-attr">"usedHeapSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">4059096</span><span class="hljs-punctuation">,</span> 13361cb0ef41Sopenharmony_ci <span class="hljs-attr">"heapSizeLimit"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">4345298944</span><span class="hljs-punctuation">,</span> 13371cb0ef41Sopenharmony_ci <span class="hljs-attr">"mallocedMemory"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">254128</span><span class="hljs-punctuation">,</span> 13381cb0ef41Sopenharmony_ci <span class="hljs-attr">"externalMemory"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">225138</span><span class="hljs-punctuation">,</span> 13391cb0ef41Sopenharmony_ci <span class="hljs-attr">"peakMallocedMemory"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">181760</span> 13401cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 13411cb0ef41Sopenharmony_ci <span class="hljs-attr">"heapSpaceStatistics"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">[</span> 13421cb0ef41Sopenharmony_ci <span class="hljs-punctuation">{</span> 13431cb0ef41Sopenharmony_ci <span class="hljs-attr">"spaceName"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"read_only_space"</span><span class="hljs-punctuation">,</span> 13441cb0ef41Sopenharmony_ci <span class="hljs-attr">"spaceSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 13451cb0ef41Sopenharmony_ci <span class="hljs-attr">"spaceUsedSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 13461cb0ef41Sopenharmony_ci <span class="hljs-attr">"spaceAvailableSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span><span class="hljs-punctuation">,</span> 13471cb0ef41Sopenharmony_ci <span class="hljs-attr">"physicalSpaceSize"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">0</span> 13481cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span> 13491cb0ef41Sopenharmony_ci <span class="hljs-punctuation">]</span> 13501cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span> 13511cb0ef41Sopenharmony_ci <span class="hljs-punctuation">}</span> 13521cb0ef41Sopenharmony_ci <span class="hljs-punctuation">]</span><span class="hljs-punctuation">,</span> 13531cb0ef41Sopenharmony_ci <span class="hljs-attr">"endTime"</span><span class="hljs-punctuation">:</span> <span class="hljs-number">1674059036865</span> 13541cb0ef41Sopenharmony_ci<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre> 13551cb0ef41Sopenharmony_ci<p>Here's an example.</p> 13561cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">GCProfiler</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'v8'</span>); 13571cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> profiler = <span class="hljs-keyword">new</span> <span class="hljs-title class_">GCProfiler</span>(); 13581cb0ef41Sopenharmony_ciprofiler.<span class="hljs-title function_">start</span>(); 13591cb0ef41Sopenharmony_ci<span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { 13601cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(profiler.<span class="hljs-title function_">stop</span>()); 13611cb0ef41Sopenharmony_ci}, <span class="hljs-number">1000</span>);</code> <button class="copy-button">copy</button></pre></section> 13621cb0ef41Sopenharmony_ci <!-- API END --> 13631cb0ef41Sopenharmony_ci </div> 13641cb0ef41Sopenharmony_ci </div> 13651cb0ef41Sopenharmony_ci </div> 13661cb0ef41Sopenharmony_ci</body> 13671cb0ef41Sopenharmony_ci</html> 1368