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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><span class="stability_0"><a href="#domain">Domain</a></span> 1241cb0ef41Sopenharmony_ci<ul> 1251cb0ef41Sopenharmony_ci<li><a href="#warning-dont-ignore-errors">Warning: Don't ignore errors!</a></li> 1261cb0ef41Sopenharmony_ci<li><a href="#additions-to-error-objects">Additions to <code>Error</code> objects</a></li> 1271cb0ef41Sopenharmony_ci<li><a href="#implicit-binding">Implicit binding</a></li> 1281cb0ef41Sopenharmony_ci<li><a href="#explicit-binding">Explicit binding</a></li> 1291cb0ef41Sopenharmony_ci<li><a href="#domaincreate"><code>domain.create()</code></a></li> 1301cb0ef41Sopenharmony_ci<li><a href="#class-domain">Class: <code>Domain</code></a> 1311cb0ef41Sopenharmony_ci<ul> 1321cb0ef41Sopenharmony_ci<li><a href="#domainmembers"><code>domain.members</code></a></li> 1331cb0ef41Sopenharmony_ci<li><a href="#domainaddemitter"><code>domain.add(emitter)</code></a></li> 1341cb0ef41Sopenharmony_ci<li><a href="#domainbindcallback"><code>domain.bind(callback)</code></a></li> 1351cb0ef41Sopenharmony_ci<li><a href="#domainenter"><code>domain.enter()</code></a></li> 1361cb0ef41Sopenharmony_ci<li><a href="#domainexit"><code>domain.exit()</code></a></li> 1371cb0ef41Sopenharmony_ci<li><a href="#domaininterceptcallback"><code>domain.intercept(callback)</code></a></li> 1381cb0ef41Sopenharmony_ci<li><a href="#domainremoveemitter"><code>domain.remove(emitter)</code></a></li> 1391cb0ef41Sopenharmony_ci<li><a href="#domainrunfn-args"><code>domain.run(fn[, ...args])</code></a></li> 1401cb0ef41Sopenharmony_ci</ul> 1411cb0ef41Sopenharmony_ci</li> 1421cb0ef41Sopenharmony_ci<li><a href="#domains-and-promises">Domains and promises</a></li> 1431cb0ef41Sopenharmony_ci</ul> 1441cb0ef41Sopenharmony_ci</li> 1451cb0ef41Sopenharmony_ci</ul></div></div> 1461cb0ef41Sopenharmony_ci </li> 1471cb0ef41Sopenharmony_ci 1481cb0ef41Sopenharmony_ci 1491cb0ef41Sopenharmony_ci <li class="picker-header"> 1501cb0ef41Sopenharmony_ci <a href="#"> 1511cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 1521cb0ef41Sopenharmony_ci Index 1531cb0ef41Sopenharmony_ci </a> 1541cb0ef41Sopenharmony_ci 1551cb0ef41Sopenharmony_ci <div class="picker"><ul> 1561cb0ef41Sopenharmony_ci<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> 1571cb0ef41Sopenharmony_ci<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> 1581cb0ef41Sopenharmony_ci 1591cb0ef41Sopenharmony_ci <li> 1601cb0ef41Sopenharmony_ci <a href="index.html">Index</a> 1611cb0ef41Sopenharmony_ci </li> 1621cb0ef41Sopenharmony_ci </ul> 1631cb0ef41Sopenharmony_ci 1641cb0ef41Sopenharmony_ci<hr class="line"> 1651cb0ef41Sopenharmony_ci<ul> 1661cb0ef41Sopenharmony_ci<li><a href="assert.html" class="nav-assert">Assertion testing</a></li> 1671cb0ef41Sopenharmony_ci<li><a href="async_context.html" 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2351cb0ef41Sopenharmony_ci <a href="#"> 2361cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 2371cb0ef41Sopenharmony_ci Other versions 2381cb0ef41Sopenharmony_ci </a> 2391cb0ef41Sopenharmony_ci <div class="picker"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v21.x/api/domain.html">21.x</a></li> 2401cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v20.x/api/domain.html">20.x <b>LTS</b></a></li> 2411cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v19.x/api/domain.html">19.x</a></li> 2421cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v18.x/api/domain.html">18.x <b>LTS</b></a></li> 2431cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v17.x/api/domain.html">17.x</a></li> 2441cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v16.x/api/domain.html">16.x</a></li> 2451cb0ef41Sopenharmony_ci<li><a 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2701cb0ef41Sopenharmony_ci <a href="all.html">View on single page</a> 2711cb0ef41Sopenharmony_ci </li> 2721cb0ef41Sopenharmony_ci <li> 2731cb0ef41Sopenharmony_ci <a href="domain.json">View as JSON</a> 2741cb0ef41Sopenharmony_ci </li> 2751cb0ef41Sopenharmony_ci <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/domain.md">Edit on GitHub</a></li> 2761cb0ef41Sopenharmony_ci </ul> 2771cb0ef41Sopenharmony_ci </div> 2781cb0ef41Sopenharmony_ci </li> 2791cb0ef41Sopenharmony_ci </ul> 2801cb0ef41Sopenharmony_ci </div> 2811cb0ef41Sopenharmony_ci <hr> 2821cb0ef41Sopenharmony_ci </header> 2831cb0ef41Sopenharmony_ci 2841cb0ef41Sopenharmony_ci <details id="toc" open><summary>Table of contents</summary><ul> 2851cb0ef41Sopenharmony_ci<li><span class="stability_0"><a href="#domain">Domain</a></span> 2861cb0ef41Sopenharmony_ci<ul> 2871cb0ef41Sopenharmony_ci<li><a href="#warning-dont-ignore-errors">Warning: Don't ignore errors!</a></li> 2881cb0ef41Sopenharmony_ci<li><a href="#additions-to-error-objects">Additions to <code>Error</code> objects</a></li> 2891cb0ef41Sopenharmony_ci<li><a href="#implicit-binding">Implicit binding</a></li> 2901cb0ef41Sopenharmony_ci<li><a href="#explicit-binding">Explicit binding</a></li> 2911cb0ef41Sopenharmony_ci<li><a href="#domaincreate"><code>domain.create()</code></a></li> 2921cb0ef41Sopenharmony_ci<li><a href="#class-domain">Class: <code>Domain</code></a> 2931cb0ef41Sopenharmony_ci<ul> 2941cb0ef41Sopenharmony_ci<li><a href="#domainmembers"><code>domain.members</code></a></li> 2951cb0ef41Sopenharmony_ci<li><a href="#domainaddemitter"><code>domain.add(emitter)</code></a></li> 2961cb0ef41Sopenharmony_ci<li><a href="#domainbindcallback"><code>domain.bind(callback)</code></a></li> 2971cb0ef41Sopenharmony_ci<li><a href="#domainenter"><code>domain.enter()</code></a></li> 2981cb0ef41Sopenharmony_ci<li><a href="#domainexit"><code>domain.exit()</code></a></li> 2991cb0ef41Sopenharmony_ci<li><a href="#domaininterceptcallback"><code>domain.intercept(callback)</code></a></li> 3001cb0ef41Sopenharmony_ci<li><a href="#domainremoveemitter"><code>domain.remove(emitter)</code></a></li> 3011cb0ef41Sopenharmony_ci<li><a href="#domainrunfn-args"><code>domain.run(fn[, ...args])</code></a></li> 3021cb0ef41Sopenharmony_ci</ul> 3031cb0ef41Sopenharmony_ci</li> 3041cb0ef41Sopenharmony_ci<li><a href="#domains-and-promises">Domains and promises</a></li> 3051cb0ef41Sopenharmony_ci</ul> 3061cb0ef41Sopenharmony_ci</li> 3071cb0ef41Sopenharmony_ci</ul></details> 3081cb0ef41Sopenharmony_ci 3091cb0ef41Sopenharmony_ci <div id="apicontent"> 3101cb0ef41Sopenharmony_ci <h2>Domain<span><a class="mark" href="#domain" id="domain">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain"></a></h2> 3111cb0ef41Sopenharmony_ci<div class="api_metadata"> 3121cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 3131cb0ef41Sopenharmony_ci<table> 3141cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 3151cb0ef41Sopenharmony_ci<tr><td>v8.8.0</td> 3161cb0ef41Sopenharmony_ci<td><p>Any <code>Promise</code>s created in VM contexts no longer have a <code>.domain</code> property. Their handlers are still executed in the proper domain, however, and <code>Promise</code>s created in the main context still possess a <code>.domain</code> property.</p></td></tr> 3171cb0ef41Sopenharmony_ci<tr><td>v8.0.0</td> 3181cb0ef41Sopenharmony_ci<td><p>Handlers for <code>Promise</code>s are now invoked in the domain in which the first promise of a chain was created.</p></td></tr> 3191cb0ef41Sopenharmony_ci<tr><td>v1.4.2</td> 3201cb0ef41Sopenharmony_ci<td><p><span>Deprecated since: v1.4.2</span></p></td></tr> 3211cb0ef41Sopenharmony_ci</tbody></table> 3221cb0ef41Sopenharmony_ci</details> 3231cb0ef41Sopenharmony_ci</div> 3241cb0ef41Sopenharmony_ci 3251cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated</div><p></p> 3261cb0ef41Sopenharmony_ci<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v18.20.1/lib/domain.js">lib/domain.js</a></p> 3271cb0ef41Sopenharmony_ci<p><strong>This module is pending deprecation.</strong> Once a replacement API has been 3281cb0ef41Sopenharmony_cifinalized, this module will be fully deprecated. Most developers should 3291cb0ef41Sopenharmony_ci<strong>not</strong> have cause to use this module. Users who absolutely must have 3301cb0ef41Sopenharmony_cithe functionality that domains provide may rely on it for the time being 3311cb0ef41Sopenharmony_cibut should expect to have to migrate to a different solution 3321cb0ef41Sopenharmony_ciin the future.</p> 3331cb0ef41Sopenharmony_ci<p>Domains provide a way to handle multiple different IO operations as a 3341cb0ef41Sopenharmony_cisingle group. If any of the event emitters or callbacks registered to a 3351cb0ef41Sopenharmony_cidomain emit an <code>'error'</code> event, or throw an error, then the domain object 3361cb0ef41Sopenharmony_ciwill be notified, rather than losing the context of the error in the 3371cb0ef41Sopenharmony_ci<code>process.on('uncaughtException')</code> handler, or causing the program to 3381cb0ef41Sopenharmony_ciexit immediately with an error code.</p> 3391cb0ef41Sopenharmony_ci<section><h3>Warning: Don't ignore errors!<span><a class="mark" href="#warning-dont-ignore-errors" id="warning-dont-ignore-errors">#</a></span><a aria-hidden="true" class="legacy" id="domain_warning_don_t_ignore_errors"></a></h3> 3401cb0ef41Sopenharmony_ci 3411cb0ef41Sopenharmony_ci<p>Domain error handlers are not a substitute for closing down a 3421cb0ef41Sopenharmony_ciprocess when an error occurs.</p> 3431cb0ef41Sopenharmony_ci<p>By the very nature of how <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/throw"><code>throw</code></a> works in JavaScript, there is almost 3441cb0ef41Sopenharmony_cinever any way to safely "pick up where it left off", without leaking 3451cb0ef41Sopenharmony_cireferences, or creating some other sort of undefined brittle state.</p> 3461cb0ef41Sopenharmony_ci<p>The safest way to respond to a thrown error is to shut down the 3471cb0ef41Sopenharmony_ciprocess. Of course, in a normal web server, there may be many 3481cb0ef41Sopenharmony_ciopen connections, and it is not reasonable to abruptly shut those down 3491cb0ef41Sopenharmony_cibecause an error was triggered by someone else.</p> 3501cb0ef41Sopenharmony_ci<p>The better approach is to send an error response to the request that 3511cb0ef41Sopenharmony_citriggered the error, while letting the others finish in their normal 3521cb0ef41Sopenharmony_citime, and stop listening for new requests in that worker.</p> 3531cb0ef41Sopenharmony_ci<p>In this way, <code>domain</code> usage goes hand-in-hand with the cluster module, 3541cb0ef41Sopenharmony_cisince the primary process can fork a new worker when a worker 3551cb0ef41Sopenharmony_ciencounters an error. For Node.js programs that scale to multiple 3561cb0ef41Sopenharmony_cimachines, the terminating proxy or service registry can take note of 3571cb0ef41Sopenharmony_cithe failure, and react accordingly.</p> 3581cb0ef41Sopenharmony_ci<p>For example, this is not a good idea:</p> 3591cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-comment">// XXX WARNING! BAD IDEA!</span> 3601cb0ef41Sopenharmony_ci 3611cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> d = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:domain'</span>).<span class="hljs-title function_">create</span>(); 3621cb0ef41Sopenharmony_cid.<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">er</span>) =></span> { 3631cb0ef41Sopenharmony_ci <span class="hljs-comment">// The error won't crash the process, but what it does is worse!</span> 3641cb0ef41Sopenharmony_ci <span class="hljs-comment">// Though we've prevented abrupt process restarting, we are leaking</span> 3651cb0ef41Sopenharmony_ci <span class="hljs-comment">// a lot of resources if this ever happens.</span> 3661cb0ef41Sopenharmony_ci <span class="hljs-comment">// This is no better than process.on('uncaughtException')!</span> 3671cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`error, but oh well <span class="hljs-subst">${er.message}</span>`</span>); 3681cb0ef41Sopenharmony_ci}); 3691cb0ef41Sopenharmony_cid.<span class="hljs-title function_">run</span>(<span class="hljs-function">() =></span> { 3701cb0ef41Sopenharmony_ci <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>).<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 3711cb0ef41Sopenharmony_ci <span class="hljs-title function_">handleRequest</span>(req, res); 3721cb0ef41Sopenharmony_ci }).<span class="hljs-title function_">listen</span>(<span class="hljs-variable constant_">PORT</span>); 3731cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 3741cb0ef41Sopenharmony_ci<p>By using the context of a domain, and the resilience of separating our 3751cb0ef41Sopenharmony_ciprogram into multiple worker processes, we can react more 3761cb0ef41Sopenharmony_ciappropriately, and handle errors with much greater safety.</p> 3771cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-comment">// Much better!</span> 3781cb0ef41Sopenharmony_ci 3791cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:cluster'</span>); 3801cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> <span class="hljs-variable constant_">PORT</span> = +process.<span class="hljs-property">env</span>.<span class="hljs-property">PORT</span> || <span class="hljs-number">1337</span>; 3811cb0ef41Sopenharmony_ci 3821cb0ef41Sopenharmony_ci<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 3831cb0ef41Sopenharmony_ci <span class="hljs-comment">// A more realistic scenario would have more than 2 workers,</span> 3841cb0ef41Sopenharmony_ci <span class="hljs-comment">// and perhaps not put the primary and worker in the same file.</span> 3851cb0ef41Sopenharmony_ci <span class="hljs-comment">//</span> 3861cb0ef41Sopenharmony_ci <span class="hljs-comment">// It is also possible to get a bit fancier about logging, and</span> 3871cb0ef41Sopenharmony_ci <span class="hljs-comment">// implement whatever custom logic is needed to prevent DoS</span> 3881cb0ef41Sopenharmony_ci <span class="hljs-comment">// attacks and other bad behavior.</span> 3891cb0ef41Sopenharmony_ci <span class="hljs-comment">//</span> 3901cb0ef41Sopenharmony_ci <span class="hljs-comment">// See the options in the cluster documentation.</span> 3911cb0ef41Sopenharmony_ci <span class="hljs-comment">//</span> 3921cb0ef41Sopenharmony_ci <span class="hljs-comment">// The important thing is that the primary does very little,</span> 3931cb0ef41Sopenharmony_ci <span class="hljs-comment">// increasing our resilience to unexpected errors.</span> 3941cb0ef41Sopenharmony_ci 3951cb0ef41Sopenharmony_ci cluster.<span class="hljs-title function_">fork</span>(); 3961cb0ef41Sopenharmony_ci cluster.<span class="hljs-title function_">fork</span>(); 3971cb0ef41Sopenharmony_ci 3981cb0ef41Sopenharmony_ci cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'disconnect'</span>, <span class="hljs-function">(<span class="hljs-params">worker</span>) =></span> { 3991cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">'disconnect!'</span>); 4001cb0ef41Sopenharmony_ci cluster.<span class="hljs-title function_">fork</span>(); 4011cb0ef41Sopenharmony_ci }); 4021cb0ef41Sopenharmony_ci 4031cb0ef41Sopenharmony_ci} <span class="hljs-keyword">else</span> { 4041cb0ef41Sopenharmony_ci <span class="hljs-comment">// the worker</span> 4051cb0ef41Sopenharmony_ci <span class="hljs-comment">//</span> 4061cb0ef41Sopenharmony_ci <span class="hljs-comment">// This is where we put our bugs!</span> 4071cb0ef41Sopenharmony_ci 4081cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> domain = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:domain'</span>); 4091cb0ef41Sopenharmony_ci 4101cb0ef41Sopenharmony_ci <span class="hljs-comment">// See the cluster documentation for more details about using</span> 4111cb0ef41Sopenharmony_ci <span class="hljs-comment">// worker processes to serve requests. How it works, caveats, etc.</span> 4121cb0ef41Sopenharmony_ci 4131cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> server = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>).<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 4141cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> d = domain.<span class="hljs-title function_">create</span>(); 4151cb0ef41Sopenharmony_ci d.<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">er</span>) =></span> { 4161cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">`error <span class="hljs-subst">${er.stack}</span>`</span>); 4171cb0ef41Sopenharmony_ci 4181cb0ef41Sopenharmony_ci <span class="hljs-comment">// We're in dangerous territory!</span> 4191cb0ef41Sopenharmony_ci <span class="hljs-comment">// By definition, something unexpected occurred,</span> 4201cb0ef41Sopenharmony_ci <span class="hljs-comment">// which we probably didn't want.</span> 4211cb0ef41Sopenharmony_ci <span class="hljs-comment">// Anything can happen now! Be very careful!</span> 4221cb0ef41Sopenharmony_ci 4231cb0ef41Sopenharmony_ci <span class="hljs-keyword">try</span> { 4241cb0ef41Sopenharmony_ci <span class="hljs-comment">// Make sure we close down within 30 seconds</span> 4251cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> killtimer = <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { 4261cb0ef41Sopenharmony_ci process.<span class="hljs-title function_">exit</span>(<span class="hljs-number">1</span>); 4271cb0ef41Sopenharmony_ci }, <span class="hljs-number">30000</span>); 4281cb0ef41Sopenharmony_ci <span class="hljs-comment">// But don't keep the process open just for that!</span> 4291cb0ef41Sopenharmony_ci killtimer.<span class="hljs-title function_">unref</span>(); 4301cb0ef41Sopenharmony_ci 4311cb0ef41Sopenharmony_ci <span class="hljs-comment">// Stop taking new requests.</span> 4321cb0ef41Sopenharmony_ci server.<span class="hljs-title function_">close</span>(); 4331cb0ef41Sopenharmony_ci 4341cb0ef41Sopenharmony_ci <span class="hljs-comment">// Let the primary know we're dead. This will trigger a</span> 4351cb0ef41Sopenharmony_ci <span class="hljs-comment">// 'disconnect' in the cluster primary, and then it will fork</span> 4361cb0ef41Sopenharmony_ci <span class="hljs-comment">// a new worker.</span> 4371cb0ef41Sopenharmony_ci cluster.<span class="hljs-property">worker</span>.<span class="hljs-title function_">disconnect</span>(); 4381cb0ef41Sopenharmony_ci 4391cb0ef41Sopenharmony_ci <span class="hljs-comment">// Try to send an error to the request that triggered the problem</span> 4401cb0ef41Sopenharmony_ci res.<span class="hljs-property">statusCode</span> = <span class="hljs-number">500</span>; 4411cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">setHeader</span>(<span class="hljs-string">'content-type'</span>, <span class="hljs-string">'text/plain'</span>); 4421cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(<span class="hljs-string">'Oops, there was a problem!\n'</span>); 4431cb0ef41Sopenharmony_ci } <span class="hljs-keyword">catch</span> (er2) { 4441cb0ef41Sopenharmony_ci <span class="hljs-comment">// Oh well, not much we can do at this point.</span> 4451cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">`Error sending 500! <span class="hljs-subst">${er2.stack}</span>`</span>); 4461cb0ef41Sopenharmony_ci } 4471cb0ef41Sopenharmony_ci }); 4481cb0ef41Sopenharmony_ci 4491cb0ef41Sopenharmony_ci <span class="hljs-comment">// Because req and res were created before this domain existed,</span> 4501cb0ef41Sopenharmony_ci <span class="hljs-comment">// we need to explicitly add them.</span> 4511cb0ef41Sopenharmony_ci <span class="hljs-comment">// See the explanation of implicit vs explicit binding below.</span> 4521cb0ef41Sopenharmony_ci d.<span class="hljs-title function_">add</span>(req); 4531cb0ef41Sopenharmony_ci d.<span class="hljs-title function_">add</span>(res); 4541cb0ef41Sopenharmony_ci 4551cb0ef41Sopenharmony_ci <span class="hljs-comment">// Now run the handler function in the domain.</span> 4561cb0ef41Sopenharmony_ci d.<span class="hljs-title function_">run</span>(<span class="hljs-function">() =></span> { 4571cb0ef41Sopenharmony_ci <span class="hljs-title function_">handleRequest</span>(req, res); 4581cb0ef41Sopenharmony_ci }); 4591cb0ef41Sopenharmony_ci }); 4601cb0ef41Sopenharmony_ci server.<span class="hljs-title function_">listen</span>(<span class="hljs-variable constant_">PORT</span>); 4611cb0ef41Sopenharmony_ci} 4621cb0ef41Sopenharmony_ci 4631cb0ef41Sopenharmony_ci<span class="hljs-comment">// This part is not important. Just an example routing thing.</span> 4641cb0ef41Sopenharmony_ci<span class="hljs-comment">// Put fancy application logic here.</span> 4651cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">handleRequest</span>(<span class="hljs-params">req, res</span>) { 4661cb0ef41Sopenharmony_ci <span class="hljs-keyword">switch</span> (req.<span class="hljs-property">url</span>) { 4671cb0ef41Sopenharmony_ci <span class="hljs-keyword">case</span> <span class="hljs-string">'/error'</span>: 4681cb0ef41Sopenharmony_ci <span class="hljs-comment">// We do some async stuff, and then...</span> 4691cb0ef41Sopenharmony_ci <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { 4701cb0ef41Sopenharmony_ci <span class="hljs-comment">// Whoops!</span> 4711cb0ef41Sopenharmony_ci flerb.<span class="hljs-title function_">bark</span>(); 4721cb0ef41Sopenharmony_ci }, timeout); 4731cb0ef41Sopenharmony_ci <span class="hljs-keyword">break</span>; 4741cb0ef41Sopenharmony_ci <span class="hljs-attr">default</span>: 4751cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(<span class="hljs-string">'ok'</span>); 4761cb0ef41Sopenharmony_ci } 4771cb0ef41Sopenharmony_ci}</code> <button class="copy-button">copy</button></pre> 4781cb0ef41Sopenharmony_ci</section><section><h3>Additions to <code>Error</code> objects<span><a class="mark" href="#additions-to-error-objects" id="additions-to-error-objects">#</a></span><a aria-hidden="true" class="legacy" id="domain_additions_to_error_objects"></a></h3> 4791cb0ef41Sopenharmony_ci 4801cb0ef41Sopenharmony_ci<p>Any time an <code>Error</code> object is routed through a domain, a few extra fields 4811cb0ef41Sopenharmony_ciare added to it.</p> 4821cb0ef41Sopenharmony_ci<ul> 4831cb0ef41Sopenharmony_ci<li><code>error.domain</code> The domain that first handled the error.</li> 4841cb0ef41Sopenharmony_ci<li><code>error.domainEmitter</code> The event emitter that emitted an <code>'error'</code> event 4851cb0ef41Sopenharmony_ciwith the error object.</li> 4861cb0ef41Sopenharmony_ci<li><code>error.domainBound</code> The callback function which was bound to the 4871cb0ef41Sopenharmony_cidomain, and passed an error as its first argument.</li> 4881cb0ef41Sopenharmony_ci<li><code>error.domainThrown</code> A boolean indicating whether the error was 4891cb0ef41Sopenharmony_cithrown, emitted, or passed to a bound callback function.</li> 4901cb0ef41Sopenharmony_ci</ul> 4911cb0ef41Sopenharmony_ci</section><section><h3>Implicit binding<span><a class="mark" href="#implicit-binding" id="implicit-binding">#</a></span><a aria-hidden="true" class="legacy" id="domain_implicit_binding"></a></h3> 4921cb0ef41Sopenharmony_ci 4931cb0ef41Sopenharmony_ci<p>If domains are in use, then all <strong>new</strong> <code>EventEmitter</code> objects (including 4941cb0ef41Sopenharmony_ciStream objects, requests, responses, etc.) will be implicitly bound to 4951cb0ef41Sopenharmony_cithe active domain at the time of their creation.</p> 4961cb0ef41Sopenharmony_ci<p>Additionally, callbacks passed to low-level event loop requests (such as 4971cb0ef41Sopenharmony_cito <code>fs.open()</code>, or other callback-taking methods) will automatically be 4981cb0ef41Sopenharmony_cibound to the active domain. If they throw, then the domain will catch 4991cb0ef41Sopenharmony_cithe error.</p> 5001cb0ef41Sopenharmony_ci<p>In order to prevent excessive memory usage, <code>Domain</code> objects themselves 5011cb0ef41Sopenharmony_ciare not implicitly added as children of the active domain. If they 5021cb0ef41Sopenharmony_ciwere, then it would be too easy to prevent request and response objects 5031cb0ef41Sopenharmony_cifrom being properly garbage collected.</p> 5041cb0ef41Sopenharmony_ci<p>To nest <code>Domain</code> objects as children of a parent <code>Domain</code> they must be 5051cb0ef41Sopenharmony_ciexplicitly added.</p> 5061cb0ef41Sopenharmony_ci<p>Implicit binding routes thrown errors and <code>'error'</code> events to the 5071cb0ef41Sopenharmony_ci<code>Domain</code>'s <code>'error'</code> event, but does not register the <code>EventEmitter</code> on the 5081cb0ef41Sopenharmony_ci<code>Domain</code>. 5091cb0ef41Sopenharmony_ciImplicit binding only takes care of thrown errors and <code>'error'</code> events.</p> 5101cb0ef41Sopenharmony_ci</section><section><h3>Explicit binding<span><a class="mark" href="#explicit-binding" id="explicit-binding">#</a></span><a aria-hidden="true" class="legacy" id="domain_explicit_binding"></a></h3> 5111cb0ef41Sopenharmony_ci 5121cb0ef41Sopenharmony_ci<p>Sometimes, the domain in use is not the one that ought to be used for a 5131cb0ef41Sopenharmony_cispecific event emitter. Or, the event emitter could have been created 5141cb0ef41Sopenharmony_ciin the context of one domain, but ought to instead be bound to some 5151cb0ef41Sopenharmony_ciother domain.</p> 5161cb0ef41Sopenharmony_ci<p>For example, there could be one domain in use for an HTTP server, but 5171cb0ef41Sopenharmony_ciperhaps we would like to have a separate domain to use for each request.</p> 5181cb0ef41Sopenharmony_ci<p>That is possible via explicit binding.</p> 5191cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-comment">// Create a top-level domain for the server</span> 5201cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> domain = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:domain'</span>); 5211cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> http = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>); 5221cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> serverDomain = domain.<span class="hljs-title function_">create</span>(); 5231cb0ef41Sopenharmony_ci 5241cb0ef41Sopenharmony_ciserverDomain.<span class="hljs-title function_">run</span>(<span class="hljs-function">() =></span> { 5251cb0ef41Sopenharmony_ci <span class="hljs-comment">// Server is created in the scope of serverDomain</span> 5261cb0ef41Sopenharmony_ci http.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 5271cb0ef41Sopenharmony_ci <span class="hljs-comment">// Req and res are also created in the scope of serverDomain</span> 5281cb0ef41Sopenharmony_ci <span class="hljs-comment">// however, we'd prefer to have a separate domain for each request.</span> 5291cb0ef41Sopenharmony_ci <span class="hljs-comment">// create it first thing, and add req and res to it.</span> 5301cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> reqd = domain.<span class="hljs-title function_">create</span>(); 5311cb0ef41Sopenharmony_ci reqd.<span class="hljs-title function_">add</span>(req); 5321cb0ef41Sopenharmony_ci reqd.<span class="hljs-title function_">add</span>(res); 5331cb0ef41Sopenharmony_ci reqd.<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">er</span>) =></span> { 5341cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">'Error'</span>, er, req.<span class="hljs-property">url</span>); 5351cb0ef41Sopenharmony_ci <span class="hljs-keyword">try</span> { 5361cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">writeHead</span>(<span class="hljs-number">500</span>); 5371cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(<span class="hljs-string">'Error occurred, sorry.'</span>); 5381cb0ef41Sopenharmony_ci } <span class="hljs-keyword">catch</span> (er2) { 5391cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">'Error sending 500'</span>, er2, req.<span class="hljs-property">url</span>); 5401cb0ef41Sopenharmony_ci } 5411cb0ef41Sopenharmony_ci }); 5421cb0ef41Sopenharmony_ci }).<span class="hljs-title function_">listen</span>(<span class="hljs-number">1337</span>); 5431cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 5441cb0ef41Sopenharmony_ci</section><section><h3><code>domain.create()</code><span><a class="mark" href="#domaincreate" id="domaincreate">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_create"></a></h3> 5451cb0ef41Sopenharmony_ci<ul> 5461cb0ef41Sopenharmony_ci<li>Returns: <a href="domain.html#class-domain" class="type"><Domain></a></li> 5471cb0ef41Sopenharmony_ci</ul> 5481cb0ef41Sopenharmony_ci</section><section><h3>Class: <code>Domain</code><span><a class="mark" href="#class-domain" id="class-domain">#</a></span><a aria-hidden="true" class="legacy" id="domain_class_domain"></a></h3> 5491cb0ef41Sopenharmony_ci<ul> 5501cb0ef41Sopenharmony_ci<li>Extends: <a href="events.html#class-eventemitter" class="type"><EventEmitter></a></li> 5511cb0ef41Sopenharmony_ci</ul> 5521cb0ef41Sopenharmony_ci<p>The <code>Domain</code> class encapsulates the functionality of routing errors and 5531cb0ef41Sopenharmony_ciuncaught exceptions to the active <code>Domain</code> object.</p> 5541cb0ef41Sopenharmony_ci<p>To handle the errors that it catches, listen to its <code>'error'</code> event.</p> 5551cb0ef41Sopenharmony_ci<h4><code>domain.members</code><span><a class="mark" href="#domainmembers" id="domainmembers">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_members"></a></h4> 5561cb0ef41Sopenharmony_ci<ul> 5571cb0ef41Sopenharmony_ci<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a></li> 5581cb0ef41Sopenharmony_ci</ul> 5591cb0ef41Sopenharmony_ci<p>An array of timers and event emitters that have been explicitly added 5601cb0ef41Sopenharmony_cito the domain.</p> 5611cb0ef41Sopenharmony_ci<h4><code>domain.add(emitter)</code><span><a class="mark" href="#domainaddemitter" id="domainaddemitter">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_add_emitter"></a></h4> 5621cb0ef41Sopenharmony_ci<ul> 5631cb0ef41Sopenharmony_ci<li><code>emitter</code> <a href="events.html#class-eventemitter" class="type"><EventEmitter></a> | <a href="timers.html#timers" class="type"><Timer></a> emitter or timer to be added to the domain</li> 5641cb0ef41Sopenharmony_ci</ul> 5651cb0ef41Sopenharmony_ci<p>Explicitly adds an emitter to the domain. If any event handlers called by 5661cb0ef41Sopenharmony_cithe emitter throw an error, or if the emitter emits an <code>'error'</code> event, it 5671cb0ef41Sopenharmony_ciwill be routed to the domain's <code>'error'</code> event, just like with implicit 5681cb0ef41Sopenharmony_cibinding.</p> 5691cb0ef41Sopenharmony_ci<p>This also works with timers that are returned from <a href="timers.html#setintervalcallback-delay-args"><code>setInterval()</code></a> and 5701cb0ef41Sopenharmony_ci<a href="timers.html#settimeoutcallback-delay-args"><code>setTimeout()</code></a>. If their callback function throws, it will be caught by 5711cb0ef41Sopenharmony_cithe domain <code>'error'</code> handler.</p> 5721cb0ef41Sopenharmony_ci<p>If the Timer or <code>EventEmitter</code> was already bound to a domain, it is removed 5731cb0ef41Sopenharmony_cifrom that one, and bound to this one instead.</p> 5741cb0ef41Sopenharmony_ci<h4><code>domain.bind(callback)</code><span><a class="mark" href="#domainbindcallback" id="domainbindcallback">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_bind_callback"></a></h4> 5751cb0ef41Sopenharmony_ci<ul> 5761cb0ef41Sopenharmony_ci<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The callback function</li> 5771cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The bound function</li> 5781cb0ef41Sopenharmony_ci</ul> 5791cb0ef41Sopenharmony_ci<p>The returned function will be a wrapper around the supplied callback 5801cb0ef41Sopenharmony_cifunction. When the returned function is called, any errors that are 5811cb0ef41Sopenharmony_cithrown will be routed to the domain's <code>'error'</code> event.</p> 5821cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> d = domain.<span class="hljs-title function_">create</span>(); 5831cb0ef41Sopenharmony_ci 5841cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">readSomeFile</span>(<span class="hljs-params">filename, cb</span>) { 5851cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">readFile</span>(filename, <span class="hljs-string">'utf8'</span>, d.<span class="hljs-title function_">bind</span>(<span class="hljs-function">(<span class="hljs-params">er, data</span>) =></span> { 5861cb0ef41Sopenharmony_ci <span class="hljs-comment">// If this throws, it will also be passed to the domain.</span> 5871cb0ef41Sopenharmony_ci <span class="hljs-keyword">return</span> <span class="hljs-title function_">cb</span>(er, data ? <span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">parse</span>(data) : <span class="hljs-literal">null</span>); 5881cb0ef41Sopenharmony_ci })); 5891cb0ef41Sopenharmony_ci} 5901cb0ef41Sopenharmony_ci 5911cb0ef41Sopenharmony_cid.<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">er</span>) =></span> { 5921cb0ef41Sopenharmony_ci <span class="hljs-comment">// An error occurred somewhere. If we throw it now, it will crash the program</span> 5931cb0ef41Sopenharmony_ci <span class="hljs-comment">// with the normal line number and stack message.</span> 5941cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 5951cb0ef41Sopenharmony_ci<h4><code>domain.enter()</code><span><a class="mark" href="#domainenter" id="domainenter">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_enter"></a></h4> 5961cb0ef41Sopenharmony_ci<p>The <code>enter()</code> method is plumbing used by the <code>run()</code>, <code>bind()</code>, and 5971cb0ef41Sopenharmony_ci<code>intercept()</code> methods to set the active domain. It sets <code>domain.active</code> and 5981cb0ef41Sopenharmony_ci<code>process.domain</code> to the domain, and implicitly pushes the domain onto the domain 5991cb0ef41Sopenharmony_cistack managed by the domain module (see <a href="#domainexit"><code>domain.exit()</code></a> for details on the 6001cb0ef41Sopenharmony_cidomain stack). The call to <code>enter()</code> delimits the beginning of a chain of 6011cb0ef41Sopenharmony_ciasynchronous calls and I/O operations bound to a domain.</p> 6021cb0ef41Sopenharmony_ci<p>Calling <code>enter()</code> changes only the active domain, and does not alter the domain 6031cb0ef41Sopenharmony_ciitself. <code>enter()</code> and <code>exit()</code> can be called an arbitrary number of times on a 6041cb0ef41Sopenharmony_cisingle domain.</p> 6051cb0ef41Sopenharmony_ci<h4><code>domain.exit()</code><span><a class="mark" href="#domainexit" id="domainexit">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_exit"></a></h4> 6061cb0ef41Sopenharmony_ci<p>The <code>exit()</code> method exits the current domain, popping it off the domain stack. 6071cb0ef41Sopenharmony_ciAny time execution is going to switch to the context of a different chain of 6081cb0ef41Sopenharmony_ciasynchronous calls, it's important to ensure that the current domain is exited. 6091cb0ef41Sopenharmony_ciThe call to <code>exit()</code> delimits either the end of or an interruption to the chain 6101cb0ef41Sopenharmony_ciof asynchronous calls and I/O operations bound to a domain.</p> 6111cb0ef41Sopenharmony_ci<p>If there are multiple, nested domains bound to the current execution context, 6121cb0ef41Sopenharmony_ci<code>exit()</code> will exit any domains nested within this domain.</p> 6131cb0ef41Sopenharmony_ci<p>Calling <code>exit()</code> changes only the active domain, and does not alter the domain 6141cb0ef41Sopenharmony_ciitself. <code>enter()</code> and <code>exit()</code> can be called an arbitrary number of times on a 6151cb0ef41Sopenharmony_cisingle domain.</p> 6161cb0ef41Sopenharmony_ci<h4><code>domain.intercept(callback)</code><span><a class="mark" href="#domaininterceptcallback" id="domaininterceptcallback">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_intercept_callback"></a></h4> 6171cb0ef41Sopenharmony_ci<ul> 6181cb0ef41Sopenharmony_ci<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The callback function</li> 6191cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The intercepted function</li> 6201cb0ef41Sopenharmony_ci</ul> 6211cb0ef41Sopenharmony_ci<p>This method is almost identical to <a href="#domainbindcallback"><code>domain.bind(callback)</code></a>. However, in 6221cb0ef41Sopenharmony_ciaddition to catching thrown errors, it will also intercept <a href="errors.html#class-error"><code>Error</code></a> 6231cb0ef41Sopenharmony_ciobjects sent as the first argument to the function.</p> 6241cb0ef41Sopenharmony_ci<p>In this way, the common <code>if (err) return callback(err);</code> pattern can be replaced 6251cb0ef41Sopenharmony_ciwith a single error handler in a single place.</p> 6261cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> d = domain.<span class="hljs-title function_">create</span>(); 6271cb0ef41Sopenharmony_ci 6281cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">readSomeFile</span>(<span class="hljs-params">filename, cb</span>) { 6291cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">readFile</span>(filename, <span class="hljs-string">'utf8'</span>, d.<span class="hljs-title function_">intercept</span>(<span class="hljs-function">(<span class="hljs-params">data</span>) =></span> { 6301cb0ef41Sopenharmony_ci <span class="hljs-comment">// Note, the first argument is never passed to the</span> 6311cb0ef41Sopenharmony_ci <span class="hljs-comment">// callback since it is assumed to be the 'Error' argument</span> 6321cb0ef41Sopenharmony_ci <span class="hljs-comment">// and thus intercepted by the domain.</span> 6331cb0ef41Sopenharmony_ci 6341cb0ef41Sopenharmony_ci <span class="hljs-comment">// If this throws, it will also be passed to the domain</span> 6351cb0ef41Sopenharmony_ci <span class="hljs-comment">// so the error-handling logic can be moved to the 'error'</span> 6361cb0ef41Sopenharmony_ci <span class="hljs-comment">// event on the domain instead of being repeated throughout</span> 6371cb0ef41Sopenharmony_ci <span class="hljs-comment">// the program.</span> 6381cb0ef41Sopenharmony_ci <span class="hljs-keyword">return</span> <span class="hljs-title function_">cb</span>(<span class="hljs-literal">null</span>, <span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">parse</span>(data)); 6391cb0ef41Sopenharmony_ci })); 6401cb0ef41Sopenharmony_ci} 6411cb0ef41Sopenharmony_ci 6421cb0ef41Sopenharmony_cid.<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">er</span>) =></span> { 6431cb0ef41Sopenharmony_ci <span class="hljs-comment">// An error occurred somewhere. If we throw it now, it will crash the program</span> 6441cb0ef41Sopenharmony_ci <span class="hljs-comment">// with the normal line number and stack message.</span> 6451cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 6461cb0ef41Sopenharmony_ci<h4><code>domain.remove(emitter)</code><span><a class="mark" href="#domainremoveemitter" id="domainremoveemitter">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_remove_emitter"></a></h4> 6471cb0ef41Sopenharmony_ci<ul> 6481cb0ef41Sopenharmony_ci<li><code>emitter</code> <a href="events.html#class-eventemitter" class="type"><EventEmitter></a> | <a href="timers.html#timers" class="type"><Timer></a> emitter or timer to be removed from the domain</li> 6491cb0ef41Sopenharmony_ci</ul> 6501cb0ef41Sopenharmony_ci<p>The opposite of <a href="#domainaddemitter"><code>domain.add(emitter)</code></a>. Removes domain handling from the 6511cb0ef41Sopenharmony_cispecified emitter.</p> 6521cb0ef41Sopenharmony_ci<h4><code>domain.run(fn[, ...args])</code><span><a class="mark" href="#domainrunfn-args" id="domainrunfn-args">#</a></span><a aria-hidden="true" class="legacy" id="domain_domain_run_fn_args"></a></h4> 6531cb0ef41Sopenharmony_ci<ul> 6541cb0ef41Sopenharmony_ci<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 6551cb0ef41Sopenharmony_ci<li><code>...args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 6561cb0ef41Sopenharmony_ci</ul> 6571cb0ef41Sopenharmony_ci<p>Run the supplied function in the context of the domain, implicitly 6581cb0ef41Sopenharmony_cibinding all event emitters, timers, and low-level requests that are 6591cb0ef41Sopenharmony_cicreated in that context. Optionally, arguments can be passed to 6601cb0ef41Sopenharmony_cithe function.</p> 6611cb0ef41Sopenharmony_ci<p>This is the most basic way to use a domain.</p> 6621cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> domain = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:domain'</span>); 6631cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); 6641cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> d = domain.<span class="hljs-title function_">create</span>(); 6651cb0ef41Sopenharmony_cid.<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">er</span>) =></span> { 6661cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">'Caught error!'</span>, er); 6671cb0ef41Sopenharmony_ci}); 6681cb0ef41Sopenharmony_cid.<span class="hljs-title function_">run</span>(<span class="hljs-function">() =></span> { 6691cb0ef41Sopenharmony_ci process.<span class="hljs-title function_">nextTick</span>(<span class="hljs-function">() =></span> { 6701cb0ef41Sopenharmony_ci <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { <span class="hljs-comment">// Simulating some various async stuff</span> 6711cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">open</span>(<span class="hljs-string">'non-existent file'</span>, <span class="hljs-string">'r'</span>, <span class="hljs-function">(<span class="hljs-params">er, fd</span>) =></span> { 6721cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (er) <span class="hljs-keyword">throw</span> er; 6731cb0ef41Sopenharmony_ci <span class="hljs-comment">// proceed...</span> 6741cb0ef41Sopenharmony_ci }); 6751cb0ef41Sopenharmony_ci }, <span class="hljs-number">100</span>); 6761cb0ef41Sopenharmony_ci }); 6771cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 6781cb0ef41Sopenharmony_ci<p>In this example, the <code>d.on('error')</code> handler will be triggered, rather 6791cb0ef41Sopenharmony_cithan crashing the program.</p> 6801cb0ef41Sopenharmony_ci</section><section><h3>Domains and promises<span><a class="mark" href="#domains-and-promises" id="domains-and-promises">#</a></span><a aria-hidden="true" class="legacy" id="domain_domains_and_promises"></a></h3> 6811cb0ef41Sopenharmony_ci<p>As of Node.js 8.0.0, the handlers of promises are run inside the domain in 6821cb0ef41Sopenharmony_ciwhich the call to <code>.then()</code> or <code>.catch()</code> itself was made:</p> 6831cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> d1 = domain.<span class="hljs-title function_">create</span>(); 6841cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> d2 = domain.<span class="hljs-title function_">create</span>(); 6851cb0ef41Sopenharmony_ci 6861cb0ef41Sopenharmony_ci<span class="hljs-keyword">let</span> p; 6871cb0ef41Sopenharmony_cid1.<span class="hljs-title function_">run</span>(<span class="hljs-function">() =></span> { 6881cb0ef41Sopenharmony_ci p = <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">42</span>); 6891cb0ef41Sopenharmony_ci}); 6901cb0ef41Sopenharmony_ci 6911cb0ef41Sopenharmony_cid2.<span class="hljs-title function_">run</span>(<span class="hljs-function">() =></span> { 6921cb0ef41Sopenharmony_ci p.<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">v</span>) =></span> { 6931cb0ef41Sopenharmony_ci <span class="hljs-comment">// running in d2</span> 6941cb0ef41Sopenharmony_ci }); 6951cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 6961cb0ef41Sopenharmony_ci<p>A callback may be bound to a specific domain using <a href="#domainbindcallback"><code>domain.bind(callback)</code></a>:</p> 6971cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> d1 = domain.<span class="hljs-title function_">create</span>(); 6981cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> d2 = domain.<span class="hljs-title function_">create</span>(); 6991cb0ef41Sopenharmony_ci 7001cb0ef41Sopenharmony_ci<span class="hljs-keyword">let</span> p; 7011cb0ef41Sopenharmony_cid1.<span class="hljs-title function_">run</span>(<span class="hljs-function">() =></span> { 7021cb0ef41Sopenharmony_ci p = <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">42</span>); 7031cb0ef41Sopenharmony_ci}); 7041cb0ef41Sopenharmony_ci 7051cb0ef41Sopenharmony_cid2.<span class="hljs-title function_">run</span>(<span class="hljs-function">() =></span> { 7061cb0ef41Sopenharmony_ci p.<span class="hljs-title function_">then</span>(p.<span class="hljs-property">domain</span>.<span class="hljs-title function_">bind</span>(<span class="hljs-function">(<span class="hljs-params">v</span>) =></span> { 7071cb0ef41Sopenharmony_ci <span class="hljs-comment">// running in d1</span> 7081cb0ef41Sopenharmony_ci })); 7091cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 7101cb0ef41Sopenharmony_ci<p>Domains will not interfere with the error handling mechanisms for 7111cb0ef41Sopenharmony_cipromises. In other words, no <code>'error'</code> event will be emitted for unhandled 7121cb0ef41Sopenharmony_ci<code>Promise</code> rejections.</p></section> 7131cb0ef41Sopenharmony_ci <!-- API END --> 7141cb0ef41Sopenharmony_ci </div> 7151cb0ef41Sopenharmony_ci </div> 7161cb0ef41Sopenharmony_ci </div> 7171cb0ef41Sopenharmony_ci</body> 7181cb0ef41Sopenharmony_ci</html> 719