Source Code: lib/util.js
\nThe node:util module supports the needs of Node.js internal APIs. Many of the\nutilities are useful for application and module developers as well. To access\nit:
const util = require('node:util');\nTakes an async function (or a function that returns a Promise) and returns a\nfunction following the error-first callback style, i.e. taking\nan (err, value) => ... callback as the last argument. In the callback, the\nfirst argument will be the rejection reason (or null if the Promise\nresolved), and the second argument will be the resolved value.
const util = require('node:util');\n\nasync function fn() {\n return 'hello world';\n}\nconst callbackFunction = util.callbackify(fn);\n\ncallbackFunction((err, ret) => {\n if (err) throw err;\n console.log(ret);\n});\nWill print:
\nhello world\nThe callback is executed asynchronously, and will have a limited stack trace.\nIf the callback throws, the process will emit an 'uncaughtException'\nevent, and if not handled will exit.
Since null has a special meaning as the first argument to a callback, if a\nwrapped function rejects a Promise with a falsy value as a reason, the value\nis wrapped in an Error with the original value stored in a field named\nreason.
function fn() {\n return Promise.reject(null);\n}\nconst callbackFunction = util.callbackify(fn);\n\ncallbackFunction((err, ret) => {\n // When the Promise was rejected with `null` it is wrapped with an Error and\n // the original value is stored in `reason`.\n err && Object.hasOwn(err, 'reason') && err.reason === null; // true\n});\nThe util.debuglog() method is used to create a function that conditionally\nwrites debug messages to stderr based on the existence of the NODE_DEBUG\nenvironment variable. If the section name appears within the value of that\nenvironment variable, then the returned function operates similar to\nconsole.error(). If not, then the returned function is a no-op.
const util = require('node:util');\nconst debuglog = util.debuglog('foo');\n\ndebuglog('hello from foo [%d]', 123);\nIf this program is run with NODE_DEBUG=foo in the environment, then\nit will output something like:
FOO 3245: hello from foo [123]\nwhere 3245 is the process id. If it is not run with that\nenvironment variable set, then it will not print anything.
The section supports wildcard also:
const util = require('node:util');\nconst debuglog = util.debuglog('foo-bar');\n\ndebuglog('hi there, it\\'s foo-bar [%d]', 2333);\nif it is run with NODE_DEBUG=foo* in the environment, then it will output\nsomething like:
FOO-BAR 3257: hi there, it's foo-bar [2333]\nMultiple comma-separated section names may be specified in the NODE_DEBUG\nenvironment variable: NODE_DEBUG=fs,net,tls.
The optional callback argument can be used to replace the logging function\nwith a different function that doesn't have any initialization or\nunnecessary wrapping.
const util = require('node:util');\nlet debuglog = util.debuglog('internals', (debug) => {\n // Replace with a logging function that optimizes out\n // testing if the section is enabled\n debuglog = debug;\n});\nThe util.debuglog().enabled getter is used to create a test that can be used\nin conditionals based on the existence of the NODE_DEBUG environment variable.\nIf the section name appears within the value of that environment variable,\nthen the returned value will be true. If not, then the returned value will be\nfalse.
const util = require('node:util');\nconst enabled = util.debuglog('foo').enabled;\nif (enabled) {\n console.log('hello from foo [%d]', 123);\n}\nIf this program is run with NODE_DEBUG=foo in the environment, then it will\noutput something like:
hello from foo [123]\nAlias for util.debuglog. Usage allows for readability of that doesn't imply\nlogging when only using util.debuglog().enabled.
The util.deprecate() method wraps fn (which may be a function or class) in\nsuch a way that it is marked as deprecated.
const util = require('node:util');\n\nexports.obsoleteFunction = util.deprecate(() => {\n // Do something here.\n}, 'obsoleteFunction() is deprecated. Use newShinyFunction() instead.');\nWhen called, util.deprecate() will return a function that will emit a\nDeprecationWarning using the 'warning' event. The warning will\nbe emitted and printed to stderr the first time the returned function is\ncalled. After the warning is emitted, the wrapped function is called without\nemitting a warning.
If the same optional code is supplied in multiple calls to util.deprecate(),\nthe warning will be emitted only once for that code.
const util = require('node:util');\n\nconst fn1 = util.deprecate(someFunction, someMessage, 'DEP0001');\nconst fn2 = util.deprecate(someOtherFunction, someOtherMessage, 'DEP0001');\nfn1(); // Emits a deprecation warning with code DEP0001\nfn2(); // Does not emit a deprecation warning because it has the same code\nIf either the --no-deprecation or --no-warnings command-line flags are\nused, or if the process.noDeprecation property is set to true prior to\nthe first deprecation warning, the util.deprecate() method does nothing.
If the --trace-deprecation or --trace-warnings command-line flags are set,\nor the process.traceDeprecation property is set to true, a warning and a\nstack trace are printed to stderr the first time the deprecated function is\ncalled.
If the --throw-deprecation command-line flag is set, or the\nprocess.throwDeprecation property is set to true, then an exception will be\nthrown when the deprecated function is called.
The --throw-deprecation command-line flag and process.throwDeprecation\nproperty take precedence over --trace-deprecation and\nprocess.traceDeprecation.
The util.format() method returns a formatted string using the first argument\nas a printf-like format string which can contain zero or more format\nspecifiers. Each specifier is replaced with the converted value from the\ncorresponding argument. Supported specifiers are:
%s: String will be used to convert all values except BigInt, Object\nand -0. BigInt values will be represented with an n and Objects that\nhave no user defined toString function are inspected using util.inspect()\nwith options { depth: 0, colors: false, compact: 3 }.%d: Number will be used to convert all values except BigInt and\nSymbol.%i: parseInt(value, 10) is used for all values except BigInt and\nSymbol.%f: parseFloat(value) is used for all values expect Symbol.%j: JSON. Replaced with the string '[Circular]' if the argument contains\ncircular references.%o: Object. A string representation of an object with generic JavaScript\nobject formatting. Similar to util.inspect() with options\n{ showHidden: true, showProxy: true }. This will show the full object\nincluding non-enumerable properties and proxies.%O: Object. A string representation of an object with generic JavaScript\nobject formatting. Similar to util.inspect() without options. This will show\nthe full object not including non-enumerable properties and proxies.%c: CSS. This specifier is ignored and will skip any CSS passed in.%%: single percent sign ('%'). This does not consume an argument.If a specifier does not have a corresponding argument, it is not replaced:
\nutil.format('%s:%s', 'foo');\n// Returns: 'foo:%s'\nValues that are not part of the format string are formatted using\nutil.inspect() if their type is not string.
If there are more arguments passed to the util.format() method than the\nnumber of specifiers, the extra arguments are concatenated to the returned\nstring, separated by spaces:
util.format('%s:%s', 'foo', 'bar', 'baz');\n// Returns: 'foo:bar baz'\nIf the first argument does not contain a valid format specifier, util.format()\nreturns a string that is the concatenation of all arguments separated by spaces:
util.format(1, 2, 3);\n// Returns: '1 2 3'\nIf only one argument is passed to util.format(), it is returned as it is\nwithout any formatting:
util.format('%% %s');\n// Returns: '%% %s'\nutil.format() is a synchronous method that is intended as a debugging tool.\nSome input values can have a significant performance overhead that can block the\nevent loop. Use this function with care and never in a hot code path.
This function is identical to util.format(), except in that it takes\nan inspectOptions argument which specifies options that are passed along to\nutil.inspect().
util.formatWithOptions({ colors: true }, 'See object %O', { foo: 42 });\n// Returns 'See object { foo: 42 }', where `42` is colored as a number\n// when printed to a terminal.\nReturns the string name for a numeric error code that comes from a Node.js API.\nThe mapping between error codes and error names is platform-dependent.\nSee Common System Errors for the names of common errors.
\nfs.access('file/that/does/not/exist', (err) => {\n const name = util.getSystemErrorName(err.errno);\n console.error(name); // ENOENT\n});\nReturns a Map of all system error codes available from the Node.js API.\nThe mapping between error codes and error names is platform-dependent.\nSee Common System Errors for the names of common errors.
\nfs.access('file/that/does/not/exist', (err) => {\n const errorMap = util.getSystemErrorMap();\n const name = errorMap.get(err.errno);\n console.error(name); // ENOENT\n});\nUsage of util.inherits() is discouraged. Please use the ES6 class and\nextends keywords to get language level inheritance support. Also note\nthat the two styles are semantically incompatible.
Inherit the prototype methods from one constructor into another. The\nprototype of constructor will be set to a new object created from\nsuperConstructor.
This mainly adds some input validation on top of\nObject.setPrototypeOf(constructor.prototype, superConstructor.prototype).\nAs an additional convenience, superConstructor will be accessible\nthrough the constructor.super_ property.
const util = require('node:util');\nconst EventEmitter = require('node:events');\n\nfunction MyStream() {\n EventEmitter.call(this);\n}\n\nutil.inherits(MyStream, EventEmitter);\n\nMyStream.prototype.write = function(data) {\n this.emit('data', data);\n};\n\nconst stream = new MyStream();\n\nconsole.log(stream instanceof EventEmitter); // true\nconsole.log(MyStream.super_ === EventEmitter); // true\n\nstream.on('data', (data) => {\n console.log(`Received data: \"${data}\"`);\n});\nstream.write('It works!'); // Received data: \"It works!\"\nES6 example using class and extends:
const EventEmitter = require('node:events');\n\nclass MyStream extends EventEmitter {\n write(data) {\n this.emit('data', data);\n }\n}\n\nconst stream = new MyStream();\n\nstream.on('data', (data) => {\n console.log(`Received data: \"${data}\"`);\n});\nstream.write('With ES6');\nThe util.inspect() method returns a string representation of object that is\nintended for debugging. The output of util.inspect may change at any time\nand should not be depended upon programmatically. Additional options may be\npassed that alter the result.\nutil.inspect() will use the constructor's name and/or @@toStringTag to make\nan identifiable tag for an inspected value.
class Foo {\n get [Symbol.toStringTag]() {\n return 'bar';\n }\n}\n\nclass Bar {}\n\nconst baz = Object.create(null, { [Symbol.toStringTag]: { value: 'foo' } });\n\nutil.inspect(new Foo()); // 'Foo [bar] {}'\nutil.inspect(new Bar()); // 'Bar {}'\nutil.inspect(baz); // '[foo] {}'\nCircular references point to their anchor by using a reference index:
\nconst { inspect } = require('node:util');\n\nconst obj = {};\nobj.a = [obj];\nobj.b = {};\nobj.b.inner = obj.b;\nobj.b.obj = obj;\n\nconsole.log(inspect(obj));\n// <ref *1> {\n// a: [ [Circular *1] ],\n// b: <ref *2> { inner: [Circular *2], obj: [Circular *1] }\n// }\nThe following example inspects all properties of the util object:
const util = require('node:util');\n\nconsole.log(util.inspect(util, { showHidden: true, depth: null }));\nThe following example highlights the effect of the compact option:
const util = require('node:util');\n\nconst o = {\n a: [1, 2, [[\n 'Lorem ipsum dolor sit amet,\\nconsectetur adipiscing elit, sed do ' +\n 'eiusmod \\ntempor incididunt ut labore et dolore magna aliqua.',\n 'test',\n 'foo']], 4],\n b: new Map([['za', 1], ['zb', 'test']]),\n};\nconsole.log(util.inspect(o, { compact: true, depth: 5, breakLength: 80 }));\n\n// { a:\n// [ 1,\n// 2,\n// [ [ 'Lorem ipsum dolor sit amet,\\nconsectetur [...]', // A long line\n// 'test',\n// 'foo' ] ],\n// 4 ],\n// b: Map(2) { 'za' => 1, 'zb' => 'test' } }\n\n// Setting `compact` to false or an integer creates more reader friendly output.\nconsole.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 }));\n\n// {\n// a: [\n// 1,\n// 2,\n// [\n// [\n// 'Lorem ipsum dolor sit amet,\\n' +\n// 'consectetur adipiscing elit, sed do eiusmod \\n' +\n// 'tempor incididunt ut labore et dolore magna aliqua.',\n// 'test',\n// 'foo'\n// ]\n// ],\n// 4\n// ],\n// b: Map(2) {\n// 'za' => 1,\n// 'zb' => 'test'\n// }\n// }\n\n// Setting `breakLength` to e.g. 150 will print the \"Lorem ipsum\" text in a\n// single line.\nThe showHidden option allows WeakMap and WeakSet entries to be\ninspected. If there are more entries than maxArrayLength, there is no\nguarantee which entries are displayed. That means retrieving the same\nWeakSet entries twice may result in different output. Furthermore, entries\nwith no remaining strong references may be garbage collected at any time.
const { inspect } = require('node:util');\n\nconst obj = { a: 1 };\nconst obj2 = { b: 2 };\nconst weakSet = new WeakSet([obj, obj2]);\n\nconsole.log(inspect(weakSet, { showHidden: true }));\n// WeakSet { { a: 1 }, { b: 2 } }\nThe sorted option ensures that an object's property insertion order does not\nimpact the result of util.inspect().
const { inspect } = require('node:util');\nconst assert = require('node:assert');\n\nconst o1 = {\n b: [2, 3, 1],\n a: '`a` comes before `b`',\n c: new Set([2, 3, 1]),\n};\nconsole.log(inspect(o1, { sorted: true }));\n// { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set(3) { 1, 2, 3 } }\nconsole.log(inspect(o1, { sorted: (a, b) => b.localeCompare(a) }));\n// { c: Set(3) { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' }\n\nconst o2 = {\n c: new Set([2, 1, 3]),\n a: '`a` comes before `b`',\n b: [2, 3, 1],\n};\nassert.strict.equal(\n inspect(o1, { sorted: true }),\n inspect(o2, { sorted: true }),\n);\nThe numericSeparator option adds an underscore every three digits to all\nnumbers.
const { inspect } = require('node:util');\n\nconst thousand = 1_000;\nconst million = 1_000_000;\nconst bigNumber = 123_456_789n;\nconst bigDecimal = 1_234.123_45;\n\nconsole.log(thousand, million, bigNumber, bigDecimal);\n// 1_000 1_000_000 123_456_789n 1_234.123_45\nutil.inspect() is a synchronous method intended for debugging. Its maximum\noutput length is approximately 128 MiB. Inputs that result in longer output will\nbe truncated.
The util.inspect() method returns a string representation of object that is\nintended for debugging. The output of util.inspect may change at any time\nand should not be depended upon programmatically. Additional options may be\npassed that alter the result.\nutil.inspect() will use the constructor's name and/or @@toStringTag to make\nan identifiable tag for an inspected value.
class Foo {\n get [Symbol.toStringTag]() {\n return 'bar';\n }\n}\n\nclass Bar {}\n\nconst baz = Object.create(null, { [Symbol.toStringTag]: { value: 'foo' } });\n\nutil.inspect(new Foo()); // 'Foo [bar] {}'\nutil.inspect(new Bar()); // 'Bar {}'\nutil.inspect(baz); // '[foo] {}'\nCircular references point to their anchor by using a reference index:
\nconst { inspect } = require('node:util');\n\nconst obj = {};\nobj.a = [obj];\nobj.b = {};\nobj.b.inner = obj.b;\nobj.b.obj = obj;\n\nconsole.log(inspect(obj));\n// <ref *1> {\n// a: [ [Circular *1] ],\n// b: <ref *2> { inner: [Circular *2], obj: [Circular *1] }\n// }\nThe following example inspects all properties of the util object:
const util = require('node:util');\n\nconsole.log(util.inspect(util, { showHidden: true, depth: null }));\nThe following example highlights the effect of the compact option:
const util = require('node:util');\n\nconst o = {\n a: [1, 2, [[\n 'Lorem ipsum dolor sit amet,\\nconsectetur adipiscing elit, sed do ' +\n 'eiusmod \\ntempor incididunt ut labore et dolore magna aliqua.',\n 'test',\n 'foo']], 4],\n b: new Map([['za', 1], ['zb', 'test']]),\n};\nconsole.log(util.inspect(o, { compact: true, depth: 5, breakLength: 80 }));\n\n// { a:\n// [ 1,\n// 2,\n// [ [ 'Lorem ipsum dolor sit amet,\\nconsectetur [...]', // A long line\n// 'test',\n// 'foo' ] ],\n// 4 ],\n// b: Map(2) { 'za' => 1, 'zb' => 'test' } }\n\n// Setting `compact` to false or an integer creates more reader friendly output.\nconsole.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 }));\n\n// {\n// a: [\n// 1,\n// 2,\n// [\n// [\n// 'Lorem ipsum dolor sit amet,\\n' +\n// 'consectetur adipiscing elit, sed do eiusmod \\n' +\n// 'tempor incididunt ut labore et dolore magna aliqua.',\n// 'test',\n// 'foo'\n// ]\n// ],\n// 4\n// ],\n// b: Map(2) {\n// 'za' => 1,\n// 'zb' => 'test'\n// }\n// }\n\n// Setting `breakLength` to e.g. 150 will print the \"Lorem ipsum\" text in a\n// single line.\nThe showHidden option allows WeakMap and WeakSet entries to be\ninspected. If there are more entries than maxArrayLength, there is no\nguarantee which entries are displayed. That means retrieving the same\nWeakSet entries twice may result in different output. Furthermore, entries\nwith no remaining strong references may be garbage collected at any time.
const { inspect } = require('node:util');\n\nconst obj = { a: 1 };\nconst obj2 = { b: 2 };\nconst weakSet = new WeakSet([obj, obj2]);\n\nconsole.log(inspect(weakSet, { showHidden: true }));\n// WeakSet { { a: 1 }, { b: 2 } }\nThe sorted option ensures that an object's property insertion order does not\nimpact the result of util.inspect().
const { inspect } = require('node:util');\nconst assert = require('node:assert');\n\nconst o1 = {\n b: [2, 3, 1],\n a: '`a` comes before `b`',\n c: new Set([2, 3, 1]),\n};\nconsole.log(inspect(o1, { sorted: true }));\n// { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set(3) { 1, 2, 3 } }\nconsole.log(inspect(o1, { sorted: (a, b) => b.localeCompare(a) }));\n// { c: Set(3) { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' }\n\nconst o2 = {\n c: new Set([2, 1, 3]),\n a: '`a` comes before `b`',\n b: [2, 3, 1],\n};\nassert.strict.equal(\n inspect(o1, { sorted: true }),\n inspect(o2, { sorted: true }),\n);\nThe numericSeparator option adds an underscore every three digits to all\nnumbers.
const { inspect } = require('node:util');\n\nconst thousand = 1_000;\nconst million = 1_000_000;\nconst bigNumber = 123_456_789n;\nconst bigDecimal = 1_234.123_45;\n\nconsole.log(thousand, million, bigNumber, bigDecimal);\n// 1_000 1_000_000 123_456_789n 1_234.123_45\nutil.inspect() is a synchronous method intended for debugging. Its maximum\noutput length is approximately 128 MiB. Inputs that result in longer output will\nbe truncated.
Color output (if enabled) of util.inspect is customizable globally\nvia the util.inspect.styles and util.inspect.colors properties.
util.inspect.styles is a map associating a style name to a color from\nutil.inspect.colors.
The default styles and associated colors are:
\nbigint: yellowboolean: yellowdate: magentamodule: underlinename: (no styling)null: boldnumber: yellowregexp: redspecial: cyan (e.g., Proxies)string: greensymbol: greenundefined: greyColor styling uses ANSI control codes that may not be supported on all\nterminals. To verify color support use tty.hasColors().
Predefined control codes are listed below (grouped as \"Modifiers\", \"Foreground\ncolors\", and \"Background colors\").
", "miscs": [ { "textRaw": "Modifiers", "name": "modifiers", "desc": "Modifier support varies throughout different terminals. They will mostly be\nignored, if not supported.
\nreset - Resets all (color) modifiers to their defaultsstrikeThrough, crossedout, crossedOut)hidden - Prints the text, but makes it invisible (Alias: conceal)faint)swapcolors, swapColors)doubleUnderline)blackredgreenyellowbluemagentacyanwhitegray (alias: grey, blackBright)redBrightgreenBrightyellowBrightblueBrightmagentaBrightcyanBrightwhiteBrightbgBlackbgRedbgGreenbgYellowbgBluebgMagentabgCyanbgWhitebgGray (alias: bgGrey, bgBlackBright)bgRedBrightbgGreenBrightbgYellowBrightbgBlueBrightbgMagentaBrightbgCyanBrightbgWhiteBrightObjects may also define their own\n[util.inspect.custom](depth, opts, inspect) function,\nwhich util.inspect() will invoke and use the result of when inspecting\nthe object.
const util = require('node:util');\n\nclass Box {\n constructor(value) {\n this.value = value;\n }\n\n [util.inspect.custom](depth, options, inspect) {\n if (depth < 0) {\n return options.stylize('[Box]', 'special');\n }\n\n const newOptions = Object.assign({}, options, {\n depth: options.depth === null ? null : options.depth - 1,\n });\n\n // Five space padding because that's the size of \"Box< \".\n const padding = ' '.repeat(5);\n const inner = inspect(this.value, newOptions)\n .replace(/\\n/g, `\\n${padding}`);\n return `${options.stylize('Box', 'special')}< ${inner} >`;\n }\n}\n\nconst box = new Box(true);\n\nutil.inspect(box);\n// Returns: \"Box< true >\"\nCustom [util.inspect.custom](depth, opts, inspect) functions typically return\na string but may return a value of any type that will be formatted accordingly\nby util.inspect().
const util = require('node:util');\n\nconst obj = { foo: 'this will not show up in the inspect() output' };\nobj[util.inspect.custom] = (depth) => {\n return { bar: 'baz' };\n};\n\nutil.inspect(obj);\n// Returns: \"{ bar: 'baz' }\"\nIn addition to being accessible through util.inspect.custom, this\nsymbol is registered globally and can be\naccessed in any environment as Symbol.for('nodejs.util.inspect.custom').
Using this allows code to be written in a portable fashion, so that the custom\ninspect function is used in an Node.js environment and ignored in the browser.\nThe util.inspect() function itself is passed as third argument to the custom\ninspect function to allow further portability.
const customInspectSymbol = Symbol.for('nodejs.util.inspect.custom');\n\nclass Password {\n constructor(value) {\n this.value = value;\n }\n\n toString() {\n return 'xxxxxxxx';\n }\n\n [customInspectSymbol](depth, inspectOptions, inspect) {\n return `Password <${this.toString()}>`;\n }\n}\n\nconst password = new Password('r0sebud');\nconsole.log(password);\n// Prints Password <xxxxxxxx>\nSee Custom inspection functions on Objects for more details.
", "shortDesc": "that can be used to declare custom inspect functions." }, { "textRaw": "`util.inspect.defaultOptions`", "name": "defaultOptions", "meta": { "added": [ "v6.4.0" ], "changes": [] }, "desc": "The defaultOptions value allows customization of the default options used by\nutil.inspect. This is useful for functions like console.log or\nutil.format which implicitly call into util.inspect. It shall be set to an\nobject containing one or more valid util.inspect() options. Setting\noption properties directly is also supported.
const util = require('node:util');\nconst arr = Array(101).fill(0);\n\nconsole.log(arr); // Logs the truncated array\nutil.inspect.defaultOptions.maxArrayLength = null;\nconsole.log(arr); // logs the full array\nReturns true if there is deep strict equality between val1 and val2.\nOtherwise, returns false.
See assert.deepStrictEqual() for more information about deep strict\nequality.
Provides a higher level API for command-line argument parsing than interacting\nwith process.argv directly. Takes a specification for the expected arguments\nand returns a structured object with the parsed options and positionals.
import { parseArgs } from 'node:util';\nconst args = ['-f', '--bar', 'b'];\nconst options = {\n foo: {\n type: 'boolean',\n short: 'f',\n },\n bar: {\n type: 'string',\n },\n};\nconst {\n values,\n positionals,\n} = parseArgs({ args, options });\nconsole.log(values, positionals);\n// Prints: [Object: null prototype] { foo: true, bar: 'b' } []\nconst { parseArgs } = require('node:util');\nconst args = ['-f', '--bar', 'b'];\nconst options = {\n foo: {\n type: 'boolean',\n short: 'f',\n },\n bar: {\n type: 'string',\n },\n};\nconst {\n values,\n positionals,\n} = parseArgs({ args, options });\nconsole.log(values, positionals);\n// Prints: [Object: null prototype] { foo: true, bar: 'b' } []\nutil.parseArgs is experimental and behavior may change. Join the\nconversation in pkgjs/parseargs to contribute to the design.
Detailed parse information is available for adding custom behaviors by\nspecifying tokens: true in the configuration.\nThe returned tokens have properties describing:
name <string> Long name of option.rawName <string> How option used in args, like -f of --foo.value <string> | <undefined> Option value specified in args.\nUndefined for boolean options.inlineValue <boolean> | <undefined> Whether option value specified inline,\nlike --foo=bar.value <string> The value of the positional argument in args (i.e. args[index]).The returned tokens are in the order encountered in the input args. Options\nthat appear more than once in args produce a token for each use. Short option\ngroups like -xy expand to a token for each option. So -xxx produces\nthree tokens.
For example to use the returned tokens to add support for a negated option\nlike --no-color, the tokens can be reprocessed to change the value stored\nfor the negated option.
import { parseArgs } from 'node:util';\n\nconst options = {\n 'color': { type: 'boolean' },\n 'no-color': { type: 'boolean' },\n 'logfile': { type: 'string' },\n 'no-logfile': { type: 'boolean' },\n};\nconst { values, tokens } = parseArgs({ options, tokens: true });\n\n// Reprocess the option tokens and overwrite the returned values.\ntokens\n .filter((token) => token.kind === 'option')\n .forEach((token) => {\n if (token.name.startsWith('no-')) {\n // Store foo:false for --no-foo\n const positiveName = token.name.slice(3);\n values[positiveName] = false;\n delete values[token.name];\n } else {\n // Resave value so last one wins if both --foo and --no-foo.\n values[token.name] = token.value ?? true;\n }\n });\n\nconst color = values.color;\nconst logfile = values.logfile ?? 'default.log';\n\nconsole.log({ logfile, color });\nconst { parseArgs } = require('node:util');\n\nconst options = {\n 'color': { type: 'boolean' },\n 'no-color': { type: 'boolean' },\n 'logfile': { type: 'string' },\n 'no-logfile': { type: 'boolean' },\n};\nconst { values, tokens } = parseArgs({ options, tokens: true });\n\n// Reprocess the option tokens and overwrite the returned values.\ntokens\n .filter((token) => token.kind === 'option')\n .forEach((token) => {\n if (token.name.startsWith('no-')) {\n // Store foo:false for --no-foo\n const positiveName = token.name.slice(3);\n values[positiveName] = false;\n delete values[token.name];\n } else {\n // Resave value so last one wins if both --foo and --no-foo.\n values[token.name] = token.value ?? true;\n }\n });\n\nconst color = values.color;\nconst logfile = values.logfile ?? 'default.log';\n\nconsole.log({ logfile, color });\nExample usage showing negated options, and when an option is used\nmultiple ways then last one wins.
\n$ node negate.js\n{ logfile: 'default.log', color: undefined }\n$ node negate.js --no-logfile --no-color\n{ logfile: false, color: false }\n$ node negate.js --logfile=test.log --color\n{ logfile: 'test.log', color: true }\n$ node negate.js --no-logfile --logfile=test.log --color --no-color\n{ logfile: 'test.log', color: false }\nTakes a function following the common error-first callback style, i.e. taking\nan (err, value) => ... callback as the last argument, and returns a version\nthat returns promises.
const util = require('node:util');\nconst fs = require('node:fs');\n\nconst stat = util.promisify(fs.stat);\nstat('.').then((stats) => {\n // Do something with `stats`\n}).catch((error) => {\n // Handle the error.\n});\nOr, equivalently using async functions:
const util = require('node:util');\nconst fs = require('node:fs');\n\nconst stat = util.promisify(fs.stat);\n\nasync function callStat() {\n const stats = await stat('.');\n console.log(`This directory is owned by ${stats.uid}`);\n}\nIf there is an original[util.promisify.custom] property present, promisify\nwill return its value, see Custom promisified functions.
promisify() assumes that original is a function taking a callback as its\nfinal argument in all cases. If original is not a function, promisify()\nwill throw an error. If original is a function but its last argument is not\nan error-first callback, it will still be passed an error-first\ncallback as its last argument.
Using promisify() on class methods or other methods that use this may not\nwork as expected unless handled specially:
const util = require('node:util');\n\nclass Foo {\n constructor() {\n this.a = 42;\n }\n\n bar(callback) {\n callback(null, this.a);\n }\n}\n\nconst foo = new Foo();\n\nconst naiveBar = util.promisify(foo.bar);\n// TypeError: Cannot read property 'a' of undefined\n// naiveBar().then(a => console.log(a));\n\nnaiveBar.call(foo).then((a) => console.log(a)); // '42'\n\nconst bindBar = naiveBar.bind(foo);\nbindBar().then((a) => console.log(a)); // '42'\nUsing the util.promisify.custom symbol one can override the return value of\nutil.promisify():
const util = require('node:util');\n\nfunction doSomething(foo, callback) {\n // ...\n}\n\ndoSomething[util.promisify.custom] = (foo) => {\n return getPromiseSomehow();\n};\n\nconst promisified = util.promisify(doSomething);\nconsole.log(promisified === doSomething[util.promisify.custom]);\n// prints 'true'\nThis can be useful for cases where the original function does not follow the\nstandard format of taking an error-first callback as the last argument.
\nFor example, with a function that takes in\n(foo, onSuccessCallback, onErrorCallback):
doSomething[util.promisify.custom] = (foo) => {\n return new Promise((resolve, reject) => {\n doSomething(foo, resolve, reject);\n });\n};\nIf promisify.custom is defined but is not a function, promisify() will\nthrow an error.
In addition to being accessible through util.promisify.custom, this\nsymbol is registered globally and can be\naccessed in any environment as Symbol.for('nodejs.util.promisify.custom').
For example, with a function that takes in\n(foo, onSuccessCallback, onErrorCallback):
const kCustomPromisifiedSymbol = Symbol.for('nodejs.util.promisify.custom');\n\ndoSomething[kCustomPromisifiedSymbol] = (foo) => {\n return new Promise((resolve, reject) => {\n doSomething(foo, resolve, reject);\n });\n};\nReturns str with any ANSI escape codes removed.
console.log(util.stripVTControlCharacters('\\u001B[4mvalue\\u001B[0m'));\n// Prints \"value\"\nReturns the string after replacing any surrogate code points\n(or equivalently, any unpaired surrogate code units) with the\nUnicode \"replacement character\" U+FFFD.
Creates and returns an <AbortController> instance whose <AbortSignal> is marked\nas transferable and can be used with structuredClone() or postMessage().
Marks the given <AbortSignal> as transferable so that it can be used with\nstructuredClone() and postMessage().
const signal = transferableAbortSignal(AbortSignal.timeout(100));\nconst channel = new MessageChannel();\nchannel.port2.postMessage(signal, [signal]);\nListens to abort event on the provided signal and\nreturns a promise that is fulfilled when the signal is\naborted. If the passed resource is garbage collected before the signal is\naborted, the returned promise shall remain pending indefinitely.
const { aborted } = require('node:util');\n\nconst dependent = obtainSomethingAbortable();\n\naborted(dependent.signal, dependent).then(() => {\n // Do something when dependent is aborted.\n});\n\ndependent.on('event', () => {\n dependent.abort();\n});\nimport { aborted } from 'node:util';\n\nconst dependent = obtainSomethingAbortable();\n\naborted(dependent.signal, dependent).then(() => {\n // Do something when dependent is aborted.\n});\n\ndependent.on('event', () => {\n dependent.abort();\n});\nAn implementation of the MIMEType class.
\nIn accordance with browser conventions, all properties of MIMEType objects\nare implemented as getters and setters on the class prototype, rather than as\ndata properties on the object itself.
A MIME string is a structured string containing multiple meaningful\ncomponents. When parsed, a MIMEType object is returned containing\nproperties for each of these components.
Gets and sets the type portion of the MIME.
\nimport { MIMEType } from 'node:util';\n\nconst myMIME = new MIMEType('text/javascript');\nconsole.log(myMIME.type);\n// Prints: text\nmyMIME.type = 'application';\nconsole.log(myMIME.type);\n// Prints: application\nconsole.log(String(myMIME));\n// Prints: application/javascript\nconst { MIMEType } = require('node:util');\n\nconst myMIME = new MIMEType('text/javascript');\nconsole.log(myMIME.type);\n// Prints: text\nmyMIME.type = 'application';\nconsole.log(myMIME.type);\n// Prints: application\nconsole.log(String(myMIME));\n// Prints: application/javascript\nGets and sets the subtype portion of the MIME.
\nimport { MIMEType } from 'node:util';\n\nconst myMIME = new MIMEType('text/ecmascript');\nconsole.log(myMIME.subtype);\n// Prints: ecmascript\nmyMIME.subtype = 'javascript';\nconsole.log(myMIME.subtype);\n// Prints: javascript\nconsole.log(String(myMIME));\n// Prints: text/javascript\nconst { MIMEType } = require('node:util');\n\nconst myMIME = new MIMEType('text/ecmascript');\nconsole.log(myMIME.subtype);\n// Prints: ecmascript\nmyMIME.subtype = 'javascript';\nconsole.log(myMIME.subtype);\n// Prints: javascript\nconsole.log(String(myMIME));\n// Prints: text/javascript\nGets the essence of the MIME. This property is read only.\nUse mime.type or mime.subtype to alter the MIME.
import { MIMEType } from 'node:util';\n\nconst myMIME = new MIMEType('text/javascript;key=value');\nconsole.log(myMIME.essence);\n// Prints: text/javascript\nmyMIME.type = 'application';\nconsole.log(myMIME.essence);\n// Prints: application/javascript\nconsole.log(String(myMIME));\n// Prints: application/javascript;key=value\nconst { MIMEType } = require('node:util');\n\nconst myMIME = new MIMEType('text/javascript;key=value');\nconsole.log(myMIME.essence);\n// Prints: text/javascript\nmyMIME.type = 'application';\nconsole.log(myMIME.essence);\n// Prints: application/javascript\nconsole.log(String(myMIME));\n// Prints: application/javascript;key=value\nGets the MIMEParams object representing the\nparameters of the MIME. This property is read-only. See\nMIMEParams documentation for details.
The toString() method on the MIMEType object returns the serialized MIME.
Because of the need for standard compliance, this method does not allow users\nto customize the serialization process of the MIME.
" }, { "textRaw": "`mime.toJSON()`", "type": "method", "name": "toJSON", "signatures": [ { "return": { "textRaw": "Returns: {string}", "name": "return", "type": "string" }, "params": [] } ], "desc": "Alias for mime.toString().
This method is automatically called when an MIMEType object is serialized\nwith JSON.stringify().
import { MIMEType } from 'node:util';\n\nconst myMIMES = [\n new MIMEType('image/png'),\n new MIMEType('image/gif'),\n];\nconsole.log(JSON.stringify(myMIMES));\n// Prints: [\"image/png\", \"image/gif\"]\nconst { MIMEType } = require('node:util');\n\nconst myMIMES = [\n new MIMEType('image/png'),\n new MIMEType('image/gif'),\n];\nconsole.log(JSON.stringify(myMIMES));\n// Prints: [\"image/png\", \"image/gif\"]\nCreates a new MIMEType object by parsing the input.
import { MIMEType } from 'node:util';\n\nconst myMIME = new MIMEType('text/plain');\nconst { MIMEType } = require('node:util');\n\nconst myMIME = new MIMEType('text/plain');\nA TypeError will be thrown if the input is not a valid MIME. Note\nthat an effort will be made to coerce the given values into strings. For\ninstance:
import { MIMEType } from 'node:util';\nconst myMIME = new MIMEType({ toString: () => 'text/plain' });\nconsole.log(String(myMIME));\n// Prints: text/plain\nconst { MIMEType } = require('node:util');\nconst myMIME = new MIMEType({ toString: () => 'text/plain' });\nconsole.log(String(myMIME));\n// Prints: text/plain\nThe MIMEParams API provides read and write access to the parameters of a\nMIMEType.
Remove all name-value pairs whose name is name.
Returns an iterator over each of the name-value pairs in the parameters.\nEach item of the iterator is a JavaScript Array. The first item of the array\nis the name, the second item of the array is the value.
Returns the value of the first name-value pair whose name is name. If there\nare no such pairs, null is returned.
Returns true if there is at least one name-value pair whose name is name.
Returns an iterator over the names of each name-value pair.
\nimport { MIMEType } from 'node:util';\n\nconst { params } = new MIMEType('text/plain;foo=0;bar=1');\nfor (const name of params.keys()) {\n console.log(name);\n}\n// Prints:\n// foo\n// bar\nconst { MIMEType } = require('node:util');\n\nconst { params } = new MIMEType('text/plain;foo=0;bar=1');\nfor (const name of params.keys()) {\n console.log(name);\n}\n// Prints:\n// foo\n// bar\nSets the value in the MIMEParams object associated with name to\nvalue. If there are any pre-existing name-value pairs whose names are name,\nset the first such pair's value to value.
import { MIMEType } from 'node:util';\n\nconst { params } = new MIMEType('text/plain;foo=0;bar=1');\nparams.set('foo', 'def');\nparams.set('baz', 'xyz');\nconsole.log(params.toString());\n// Prints: foo=def&bar=1&baz=xyz\nconst { MIMEType } = require('node:util');\n\nconst { params } = new MIMEType('text/plain;foo=0;bar=1');\nparams.set('foo', 'def');\nparams.set('baz', 'xyz');\nconsole.log(params.toString());\n// Prints: foo=def&bar=1&baz=xyz\nReturns an iterator over the values of each name-value pair.
" } ], "modules": [ { "textRaw": "`mimeParams[@@iterator]()`", "name": "`mimeparams[@@iterator]()`", "desc": "Alias for mimeParams.entries().
import { MIMEType } from 'node:util';\n\nconst { params } = new MIMEType('text/plain;foo=bar;xyz=baz');\nfor (const [name, value] of params) {\n console.log(name, value);\n}\n// Prints:\n// foo bar\n// xyz baz\nconst { MIMEType } = require('node:util');\n\nconst { params } = new MIMEType('text/plain;foo=bar;xyz=baz');\nfor (const [name, value] of params) {\n console.log(name, value);\n}\n// Prints:\n// foo bar\n// xyz baz\nCreates a new MIMEParams object by with empty parameters
import { MIMEParams } from 'node:util';\n\nconst myParams = new MIMEParams();\nconst { MIMEParams } = require('node:util');\n\nconst myParams = new MIMEParams();\nAn implementation of the WHATWG Encoding Standard TextDecoder API.
const decoder = new TextDecoder();\nconst u8arr = new Uint8Array([72, 101, 108, 108, 111]);\nconsole.log(decoder.decode(u8arr)); // Hello\nPer the WHATWG Encoding Standard, the encodings supported by the\nTextDecoder API are outlined in the tables below. For each encoding,\none or more aliases may be used.
Different Node.js build configurations support different sets of encodings.\n(see Internationalization)
", "modules": [ { "textRaw": "Encodings supported by default (with full ICU data)", "name": "encodings_supported_by_default_(with_full_icu_data)", "desc": "| Encoding | \nAliases | \n
|---|---|
'ibm866' | \n'866', 'cp866', 'csibm866' | \n
'iso-8859-2' | \n'csisolatin2', 'iso-ir-101', 'iso8859-2', 'iso88592', 'iso_8859-2', 'iso_8859-2:1987', 'l2', 'latin2' | \n
'iso-8859-3' | \n'csisolatin3', 'iso-ir-109', 'iso8859-3', 'iso88593', 'iso_8859-3', 'iso_8859-3:1988', 'l3', 'latin3' | \n
'iso-8859-4' | \n'csisolatin4', 'iso-ir-110', 'iso8859-4', 'iso88594', 'iso_8859-4', 'iso_8859-4:1988', 'l4', 'latin4' | \n
'iso-8859-5' | \n'csisolatincyrillic', 'cyrillic', 'iso-ir-144', 'iso8859-5', 'iso88595', 'iso_8859-5', 'iso_8859-5:1988' | \n
'iso-8859-6' | \n'arabic', 'asmo-708', 'csiso88596e', 'csiso88596i', 'csisolatinarabic', 'ecma-114', 'iso-8859-6-e', 'iso-8859-6-i', 'iso-ir-127', 'iso8859-6', 'iso88596', 'iso_8859-6', 'iso_8859-6:1987' | \n
'iso-8859-7' | \n'csisolatingreek', 'ecma-118', 'elot_928', 'greek', 'greek8', 'iso-ir-126', 'iso8859-7', 'iso88597', 'iso_8859-7', 'iso_8859-7:1987', 'sun_eu_greek' | \n
'iso-8859-8' | \n'csiso88598e', 'csisolatinhebrew', 'hebrew', 'iso-8859-8-e', 'iso-ir-138', 'iso8859-8', 'iso88598', 'iso_8859-8', 'iso_8859-8:1988', 'visual' | \n
'iso-8859-8-i' | \n'csiso88598i', 'logical' | \n
'iso-8859-10' | \n'csisolatin6', 'iso-ir-157', 'iso8859-10', 'iso885910', 'l6', 'latin6' | \n
'iso-8859-13' | \n'iso8859-13', 'iso885913' | \n
'iso-8859-14' | \n'iso8859-14', 'iso885914' | \n
'iso-8859-15' | \n'csisolatin9', 'iso8859-15', 'iso885915', 'iso_8859-15', 'l9' | \n
'koi8-r' | \n'cskoi8r', 'koi', 'koi8', 'koi8_r' | \n
'koi8-u' | \n'koi8-ru' | \n
'macintosh' | \n'csmacintosh', 'mac', 'x-mac-roman' | \n
'windows-874' | \n'dos-874', 'iso-8859-11', 'iso8859-11', 'iso885911', 'tis-620' | \n
'windows-1250' | \n'cp1250', 'x-cp1250' | \n
'windows-1251' | \n'cp1251', 'x-cp1251' | \n
'windows-1252' | \n'ansi_x3.4-1968', 'ascii', 'cp1252', 'cp819', 'csisolatin1', 'ibm819', 'iso-8859-1', 'iso-ir-100', 'iso8859-1', 'iso88591', 'iso_8859-1', 'iso_8859-1:1987', 'l1', 'latin1', 'us-ascii', 'x-cp1252' | \n
'windows-1253' | \n'cp1253', 'x-cp1253' | \n
'windows-1254' | \n'cp1254', 'csisolatin5', 'iso-8859-9', 'iso-ir-148', 'iso8859-9', 'iso88599', 'iso_8859-9', 'iso_8859-9:1989', 'l5', 'latin5', 'x-cp1254' | \n
'windows-1255' | \n'cp1255', 'x-cp1255' | \n
'windows-1256' | \n'cp1256', 'x-cp1256' | \n
'windows-1257' | \n'cp1257', 'x-cp1257' | \n
'windows-1258' | \n'cp1258', 'x-cp1258' | \n
'x-mac-cyrillic' | \n'x-mac-ukrainian' | \n
'gbk' | \n'chinese', 'csgb2312', 'csiso58gb231280', 'gb2312', 'gb_2312', 'gb_2312-80', 'iso-ir-58', 'x-gbk' | \n
'gb18030' | \n\n |
'big5' | \n'big5-hkscs', 'cn-big5', 'csbig5', 'x-x-big5' | \n
'euc-jp' | \n'cseucpkdfmtjapanese', 'x-euc-jp' | \n
'iso-2022-jp' | \n'csiso2022jp' | \n
'shift_jis' | \n'csshiftjis', 'ms932', 'ms_kanji', 'shift-jis', 'sjis', 'windows-31j', 'x-sjis' | \n
'euc-kr' | \n'cseuckr', 'csksc56011987', 'iso-ir-149', 'korean', 'ks_c_5601-1987', 'ks_c_5601-1989', 'ksc5601', 'ksc_5601', 'windows-949' | \n
| Encoding | \nAliases | \n
|---|---|
'utf-8' | \n'unicode-1-1-utf-8', 'utf8' | \n
'utf-16le' | \n'utf-16' | \n
'utf-16be' | \n\n |
| Encoding | \nAliases | \n
|---|---|
'utf-8' | \n'unicode-1-1-utf-8', 'utf8' | \n
'utf-16le' | \n'utf-16' | \n
The 'iso-8859-16' encoding listed in the WHATWG Encoding Standard\nis not supported.
Decodes the input and returns a string. If options.stream is true, any\nincomplete byte sequences occurring at the end of the input are buffered\ninternally and emitted after the next call to textDecoder.decode().
If textDecoder.fatal is true, decoding errors that occur will result in a\nTypeError being thrown.
The encoding supported by the TextDecoder instance.
The value will be true if decoding errors result in a TypeError being\nthrown.
The value will be true if the decoding result will include the byte order\nmark.
Creates a new TextDecoder instance. The encoding may specify one of the\nsupported encodings or an alias.
The TextDecoder class is also available on the global object.
An implementation of the WHATWG Encoding Standard TextEncoder API. All\ninstances of TextEncoder only support UTF-8 encoding.
const encoder = new TextEncoder();\nconst uint8array = encoder.encode('this is some data');\nThe TextEncoder class is also available on the global object.
UTF-8 encodes the input string and returns a Uint8Array containing the\nencoded bytes.
UTF-8 encodes the src string to the dest Uint8Array and returns an object\ncontaining the read Unicode code units and written UTF-8 bytes.
const encoder = new TextEncoder();\nconst src = 'this is some data';\nconst dest = new Uint8Array(10);\nconst { read, written } = encoder.encodeInto(src, dest);\nThe encoding supported by the TextEncoder instance. Always set to 'utf-8'.
util.types provides type checks for different kinds of built-in objects.\nUnlike instanceof or Object.prototype.toString.call(value), these checks do\nnot inspect properties of the object that are accessible from JavaScript (like\ntheir prototype), and usually have the overhead of calling into C++.
The result generally does not make any guarantees about what kinds of\nproperties or behavior a value exposes in JavaScript. They are primarily\nuseful for addon developers who prefer to do type checking in JavaScript.
\nThe API is accessible via require('node:util').types or require('node:util/types').
Returns true if the value is a built-in ArrayBuffer or\nSharedArrayBuffer instance.
See also util.types.isArrayBuffer() and\nutil.types.isSharedArrayBuffer().
util.types.isAnyArrayBuffer(new ArrayBuffer()); // Returns true\nutil.types.isAnyArrayBuffer(new SharedArrayBuffer()); // Returns true\nReturns true if the value is an instance of one of the ArrayBuffer\nviews, such as typed array objects or DataView. Equivalent to\nArrayBuffer.isView().
util.types.isArrayBufferView(new Int8Array()); // true\nutil.types.isArrayBufferView(Buffer.from('hello world')); // true\nutil.types.isArrayBufferView(new DataView(new ArrayBuffer(16))); // true\nutil.types.isArrayBufferView(new ArrayBuffer()); // false\nReturns true if the value is an arguments object.
function foo() {\n util.types.isArgumentsObject(arguments); // Returns true\n}\nReturns true if the value is a built-in ArrayBuffer instance.\nThis does not include SharedArrayBuffer instances. Usually, it is\ndesirable to test for both; See util.types.isAnyArrayBuffer() for that.
util.types.isArrayBuffer(new ArrayBuffer()); // Returns true\nutil.types.isArrayBuffer(new SharedArrayBuffer()); // Returns false\nReturns true if the value is an async function.\nThis only reports back what the JavaScript engine is seeing;\nin particular, the return value may not match the original source code if\na transpilation tool was used.
util.types.isAsyncFunction(function foo() {}); // Returns false\nutil.types.isAsyncFunction(async function foo() {}); // Returns true\nReturns true if the value is a BigInt64Array instance.
util.types.isBigInt64Array(new BigInt64Array()); // Returns true\nutil.types.isBigInt64Array(new BigUint64Array()); // Returns false\nReturns true if the value is a BigUint64Array instance.
util.types.isBigUint64Array(new BigInt64Array()); // Returns false\nutil.types.isBigUint64Array(new BigUint64Array()); // Returns true\nReturns true if the value is a boolean object, e.g. created\nby new Boolean().
util.types.isBooleanObject(false); // Returns false\nutil.types.isBooleanObject(true); // Returns false\nutil.types.isBooleanObject(new Boolean(false)); // Returns true\nutil.types.isBooleanObject(new Boolean(true)); // Returns true\nutil.types.isBooleanObject(Boolean(false)); // Returns false\nutil.types.isBooleanObject(Boolean(true)); // Returns false\nReturns true if the value is any boxed primitive object, e.g. created\nby new Boolean(), new String() or Object(Symbol()).
For example:
\nutil.types.isBoxedPrimitive(false); // Returns false\nutil.types.isBoxedPrimitive(new Boolean(false)); // Returns true\nutil.types.isBoxedPrimitive(Symbol('foo')); // Returns false\nutil.types.isBoxedPrimitive(Object(Symbol('foo'))); // Returns true\nutil.types.isBoxedPrimitive(Object(BigInt(5))); // Returns true\nReturns true if value is a <CryptoKey>, false otherwise.
Returns true if the value is a built-in DataView instance.
const ab = new ArrayBuffer(20);\nutil.types.isDataView(new DataView(ab)); // Returns true\nutil.types.isDataView(new Float64Array()); // Returns false\nSee also ArrayBuffer.isView().
Returns true if the value is a built-in Date instance.
util.types.isDate(new Date()); // Returns true\nReturns true if the value is a native External value.
A native External value is a special type of object that contains a\nraw C++ pointer (void*) for access from native code, and has no other\nproperties. Such objects are created either by Node.js internals or native\naddons. In JavaScript, they are frozen objects with a\nnull prototype.
#include <js_native_api.h>\n#include <stdlib.h>\nnapi_value result;\nstatic napi_value MyNapi(napi_env env, napi_callback_info info) {\n int* raw = (int*) malloc(1024);\n napi_status status = napi_create_external(env, (void*) raw, NULL, NULL, &result);\n if (status != napi_ok) {\n napi_throw_error(env, NULL, \"napi_create_external failed\");\n return NULL;\n }\n return result;\n}\n...\nDECLARE_NAPI_PROPERTY(\"myNapi\", MyNapi)\n...\nconst native = require('napi_addon.node');\nconst data = native.myNapi();\nutil.types.isExternal(data); // returns true\nutil.types.isExternal(0); // returns false\nutil.types.isExternal(new String('foo')); // returns false\nFor further information on napi_create_external, refer to\nnapi_create_external().
Returns true if the value is a built-in Float32Array instance.
util.types.isFloat32Array(new ArrayBuffer()); // Returns false\nutil.types.isFloat32Array(new Float32Array()); // Returns true\nutil.types.isFloat32Array(new Float64Array()); // Returns false\nReturns true if the value is a built-in Float64Array instance.
util.types.isFloat64Array(new ArrayBuffer()); // Returns false\nutil.types.isFloat64Array(new Uint8Array()); // Returns false\nutil.types.isFloat64Array(new Float64Array()); // Returns true\nReturns true if the value is a generator function.\nThis only reports back what the JavaScript engine is seeing;\nin particular, the return value may not match the original source code if\na transpilation tool was used.
util.types.isGeneratorFunction(function foo() {}); // Returns false\nutil.types.isGeneratorFunction(function* foo() {}); // Returns true\nReturns true if the value is a generator object as returned from a\nbuilt-in generator function.\nThis only reports back what the JavaScript engine is seeing;\nin particular, the return value may not match the original source code if\na transpilation tool was used.
function* foo() {}\nconst generator = foo();\nutil.types.isGeneratorObject(generator); // Returns true\nReturns true if the value is a built-in Int8Array instance.
util.types.isInt8Array(new ArrayBuffer()); // Returns false\nutil.types.isInt8Array(new Int8Array()); // Returns true\nutil.types.isInt8Array(new Float64Array()); // Returns false\nReturns true if the value is a built-in Int16Array instance.
util.types.isInt16Array(new ArrayBuffer()); // Returns false\nutil.types.isInt16Array(new Int16Array()); // Returns true\nutil.types.isInt16Array(new Float64Array()); // Returns false\nReturns true if the value is a built-in Int32Array instance.
util.types.isInt32Array(new ArrayBuffer()); // Returns false\nutil.types.isInt32Array(new Int32Array()); // Returns true\nutil.types.isInt32Array(new Float64Array()); // Returns false\nReturns true if value is a <KeyObject>, false otherwise.
Returns true if the value is a built-in Map instance.
util.types.isMap(new Map()); // Returns true\nReturns true if the value is an iterator returned for a built-in\nMap instance.
const map = new Map();\nutil.types.isMapIterator(map.keys()); // Returns true\nutil.types.isMapIterator(map.values()); // Returns true\nutil.types.isMapIterator(map.entries()); // Returns true\nutil.types.isMapIterator(map[Symbol.iterator]()); // Returns true\nReturns true if the value is an instance of a Module Namespace Object.
import * as ns from './a.js';\n\nutil.types.isModuleNamespaceObject(ns); // Returns true\nReturns true if the value was returned by the constructor of a\nbuilt-in Error type.
console.log(util.types.isNativeError(new Error())); // true\nconsole.log(util.types.isNativeError(new TypeError())); // true\nconsole.log(util.types.isNativeError(new RangeError())); // true\nSubclasses of the native error types are also native errors:
\nclass MyError extends Error {}\nconsole.log(util.types.isNativeError(new MyError())); // true\nA value being instanceof a native error class is not equivalent to isNativeError()\nreturning true for that value. isNativeError() returns true for errors\nwhich come from a different realm while instanceof Error returns false\nfor these errors:
const vm = require('node:vm');\nconst context = vm.createContext({});\nconst myError = vm.runInContext('new Error()', context);\nconsole.log(util.types.isNativeError(myError)); // true\nconsole.log(myError instanceof Error); // false\nConversely, isNativeError() returns false for all objects which were not\nreturned by the constructor of a native error. That includes values\nwhich are instanceof native errors:
const myError = { __proto__: Error.prototype };\nconsole.log(util.types.isNativeError(myError)); // false\nconsole.log(myError instanceof Error); // true\nReturns true if the value is a number object, e.g. created\nby new Number().
util.types.isNumberObject(0); // Returns false\nutil.types.isNumberObject(new Number(0)); // Returns true\nReturns true if the value is a built-in Promise.
util.types.isPromise(Promise.resolve(42)); // Returns true\nReturns true if the value is a Proxy instance.
const target = {};\nconst proxy = new Proxy(target, {});\nutil.types.isProxy(target); // Returns false\nutil.types.isProxy(proxy); // Returns true\nReturns true if the value is a regular expression object.
util.types.isRegExp(/abc/); // Returns true\nutil.types.isRegExp(new RegExp('abc')); // Returns true\nReturns true if the value is a built-in Set instance.
util.types.isSet(new Set()); // Returns true\nReturns true if the value is an iterator returned for a built-in\nSet instance.
const set = new Set();\nutil.types.isSetIterator(set.keys()); // Returns true\nutil.types.isSetIterator(set.values()); // Returns true\nutil.types.isSetIterator(set.entries()); // Returns true\nutil.types.isSetIterator(set[Symbol.iterator]()); // Returns true\nReturns true if the value is a built-in SharedArrayBuffer instance.\nThis does not include ArrayBuffer instances. Usually, it is\ndesirable to test for both; See util.types.isAnyArrayBuffer() for that.
util.types.isSharedArrayBuffer(new ArrayBuffer()); // Returns false\nutil.types.isSharedArrayBuffer(new SharedArrayBuffer()); // Returns true\nReturns true if the value is a string object, e.g. created\nby new String().
util.types.isStringObject('foo'); // Returns false\nutil.types.isStringObject(new String('foo')); // Returns true\nReturns true if the value is a symbol object, created\nby calling Object() on a Symbol primitive.
const symbol = Symbol('foo');\nutil.types.isSymbolObject(symbol); // Returns false\nutil.types.isSymbolObject(Object(symbol)); // Returns true\nReturns true if the value is a built-in TypedArray instance.
util.types.isTypedArray(new ArrayBuffer()); // Returns false\nutil.types.isTypedArray(new Uint8Array()); // Returns true\nutil.types.isTypedArray(new Float64Array()); // Returns true\nSee also ArrayBuffer.isView().
Returns true if the value is a built-in Uint8Array instance.
util.types.isUint8Array(new ArrayBuffer()); // Returns false\nutil.types.isUint8Array(new Uint8Array()); // Returns true\nutil.types.isUint8Array(new Float64Array()); // Returns false\nReturns true if the value is a built-in Uint8ClampedArray instance.
util.types.isUint8ClampedArray(new ArrayBuffer()); // Returns false\nutil.types.isUint8ClampedArray(new Uint8ClampedArray()); // Returns true\nutil.types.isUint8ClampedArray(new Float64Array()); // Returns false\nReturns true if the value is a built-in Uint16Array instance.
util.types.isUint16Array(new ArrayBuffer()); // Returns false\nutil.types.isUint16Array(new Uint16Array()); // Returns true\nutil.types.isUint16Array(new Float64Array()); // Returns false\nReturns true if the value is a built-in Uint32Array instance.
util.types.isUint32Array(new ArrayBuffer()); // Returns false\nutil.types.isUint32Array(new Uint32Array()); // Returns true\nutil.types.isUint32Array(new Float64Array()); // Returns false\nReturns true if the value is a built-in WeakMap instance.
util.types.isWeakMap(new WeakMap()); // Returns true\nReturns true if the value is a built-in WeakSet instance.
util.types.isWeakSet(new WeakSet()); // Returns true\nReturns true if the value is a built-in WebAssembly.Module instance.
const module = new WebAssembly.Module(wasmBuffer);\nutil.types.isWebAssemblyCompiledModule(module); // Returns true\nThe following APIs are deprecated and should no longer be used. Existing\napplications and modules should be updated to find alternative approaches.
", "methods": [ { "textRaw": "`util._extend(target, source)`", "type": "method", "name": "_extend", "meta": { "added": [ "v0.7.5" ], "deprecated": [ "v6.0.0" ], "changes": [] }, "stability": 0, "stabilityText": "Deprecated: Use [`Object.assign()`][] instead.", "signatures": [ { "params": [ { "textRaw": "`target` {Object}", "name": "target", "type": "Object" }, { "textRaw": "`source` {Object}", "name": "source", "type": "Object" } ] } ], "desc": "The util._extend() method was never intended to be used outside of internal\nNode.js modules. The community found and used it anyway.
It is deprecated and should not be used in new code. JavaScript comes with very\nsimilar built-in functionality through Object.assign().
Alias for Array.isArray().
Returns true if the given object is an Array. Otherwise, returns false.
const util = require('node:util');\n\nutil.isArray([]);\n// Returns: true\nutil.isArray(new Array());\n// Returns: true\nutil.isArray({});\n// Returns: false\nReturns true if the given object is a Boolean. Otherwise, returns false.
const util = require('node:util');\n\nutil.isBoolean(1);\n// Returns: false\nutil.isBoolean(0);\n// Returns: false\nutil.isBoolean(false);\n// Returns: true\nReturns true if the given object is a Buffer. Otherwise, returns false.
const util = require('node:util');\n\nutil.isBuffer({ length: 0 });\n// Returns: false\nutil.isBuffer([]);\n// Returns: false\nutil.isBuffer(Buffer.from('hello world'));\n// Returns: true\nReturns true if the given object is a Date. Otherwise, returns false.
const util = require('node:util');\n\nutil.isDate(new Date());\n// Returns: true\nutil.isDate(Date());\n// false (without 'new' returns a String)\nutil.isDate({});\n// Returns: false\nReturns true if the given object is an Error. Otherwise, returns\nfalse.
const util = require('node:util');\n\nutil.isError(new Error());\n// Returns: true\nutil.isError(new TypeError());\n// Returns: true\nutil.isError({ name: 'Error', message: 'an error occurred' });\n// Returns: false\nThis method relies on Object.prototype.toString() behavior. It is\npossible to obtain an incorrect result when the object argument manipulates\n@@toStringTag.
const util = require('node:util');\nconst obj = { name: 'Error', message: 'an error occurred' };\n\nutil.isError(obj);\n// Returns: false\nobj[Symbol.toStringTag] = 'Error';\nutil.isError(obj);\n// Returns: true\nReturns true if the given object is a Function. Otherwise, returns\nfalse.
const util = require('node:util');\n\nfunction Foo() {}\nconst Bar = () => {};\n\nutil.isFunction({});\n// Returns: false\nutil.isFunction(Foo);\n// Returns: true\nutil.isFunction(Bar);\n// Returns: true\nReturns true if the given object is strictly null. Otherwise, returns\nfalse.
const util = require('node:util');\n\nutil.isNull(0);\n// Returns: false\nutil.isNull(undefined);\n// Returns: false\nutil.isNull(null);\n// Returns: true\nReturns true if the given object is null or undefined. Otherwise,\nreturns false.
const util = require('node:util');\n\nutil.isNullOrUndefined(0);\n// Returns: false\nutil.isNullOrUndefined(undefined);\n// Returns: true\nutil.isNullOrUndefined(null);\n// Returns: true\nReturns true if the given object is a Number. Otherwise, returns false.
const util = require('node:util');\n\nutil.isNumber(false);\n// Returns: false\nutil.isNumber(Infinity);\n// Returns: true\nutil.isNumber(0);\n// Returns: true\nutil.isNumber(NaN);\n// Returns: true\nReturns true if the given object is strictly an Object and not a\nFunction (even though functions are objects in JavaScript).\nOtherwise, returns false.
const util = require('node:util');\n\nutil.isObject(5);\n// Returns: false\nutil.isObject(null);\n// Returns: false\nutil.isObject({});\n// Returns: true\nutil.isObject(() => {});\n// Returns: false\nReturns true if the given object is a primitive type. Otherwise, returns\nfalse.
const util = require('node:util');\n\nutil.isPrimitive(5);\n// Returns: true\nutil.isPrimitive('foo');\n// Returns: true\nutil.isPrimitive(false);\n// Returns: true\nutil.isPrimitive(null);\n// Returns: true\nutil.isPrimitive(undefined);\n// Returns: true\nutil.isPrimitive({});\n// Returns: false\nutil.isPrimitive(() => {});\n// Returns: false\nutil.isPrimitive(/^$/);\n// Returns: false\nutil.isPrimitive(new Date());\n// Returns: false\nReturns true if the given object is a RegExp. Otherwise, returns false.
const util = require('node:util');\n\nutil.isRegExp(/some regexp/);\n// Returns: true\nutil.isRegExp(new RegExp('another regexp'));\n// Returns: true\nutil.isRegExp({});\n// Returns: false\nReturns true if the given object is a string. Otherwise, returns false.
const util = require('node:util');\n\nutil.isString('');\n// Returns: true\nutil.isString('foo');\n// Returns: true\nutil.isString(String('foo'));\n// Returns: true\nutil.isString(5);\n// Returns: false\nReturns true if the given object is a Symbol. Otherwise, returns false.
const util = require('node:util');\n\nutil.isSymbol(5);\n// Returns: false\nutil.isSymbol('foo');\n// Returns: false\nutil.isSymbol(Symbol('foo'));\n// Returns: true\nReturns true if the given object is undefined. Otherwise, returns false.
const util = require('node:util');\n\nconst foo = undefined;\nutil.isUndefined(5);\n// Returns: false\nutil.isUndefined(foo);\n// Returns: true\nutil.isUndefined(null);\n// Returns: false\nThe util.log() method prints the given string to stdout with an included\ntimestamp.
const util = require('node:util');\n\nutil.log('Timestamped message.');\n