The util module is primarily designed to support the needs of Node.js' own\ninternal APIs. However, many of the utilities are useful for application and\nmodule developers as well. It can be accessed using:
const util = require('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\na (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('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 }\n const callbackFunction = util.callbackify(fn);\n\n callbackFunction((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 && err.hasOwnProperty('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('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('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 util.deprecate() method wraps the given function or class in such a way \nthat it is marked as deprecated.
const util = require('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 process.on('warning') event. By default,\nthis warning will be emitted and printed to stderr exactly once, the first\ntime it is called. After the warning is emitted, the wrapped function\nis called.
If 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.
The first argument is a string containing zero or more placeholder tokens.\nEach placeholder token is replaced with the converted value from the\ncorresponding argument. Supported placeholders are:
\n%s - String.%d - Number (integer or floating point value).%i - Integer.%f - Floating point value.%j - JSON. Replaced with the string '[Circular]' if the argument\ncontains circular references.%o - Object. A string representation of an object\nwith generic JavaScript object formatting.\nSimilar to util.inspect() with options { showHidden: true, depth: 4, \nshowProxy: true }. This will show the full object including non-enumerable \nsymbols and properties.%O - Object. A string representation of an object\nwith generic JavaScript object formatting.\nSimilar to util.inspect() without options.\nThis will show the full object not including non-enumerable symbols and \nproperties.%% - single percent sign ('%'). This does not consume an argument.If the placeholder does not have a corresponding argument, the placeholder is\nnot replaced.
\nutil.format('%s:%s', 'foo');\n// Returns: 'foo:%s'\nIf there are more arguments passed to the util.format() method than the number\nof placeholders, the extra arguments are coerced into strings then concatenated\nto the returned string, each delimited by a space. Excessive arguments whose\ntypeof is 'object' or 'symbol' (except null) will be transformed by\nutil.inspect().
util.format('%s:%s', 'foo', 'bar', 'baz'); // 'foo:bar baz'\nIf the first argument is not a string then util.format() returns\na string that is the concatenation of all arguments separated by spaces.\nEach argument is converted to a string using util.inspect().
util.format(1, 2, 3); // '1 2 3'\nIf only one argument is passed to util.format(), it is returned as it is\nwithout any formatting.
util.format('%% %s'); // '%% %s'\nPlease note that util.format() is a synchronous method that is mainly\nintended as a debugging tool. Some input values can have a significant\nperformance overhead that can block the event loop. Use this function\nwith care and never in a hot code path.
Returns 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});\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.
constructor {Function}superConstructor {Function}Inherit the prototype methods from one constructor into another. The\nprototype of constructor will be set to a new object created from\nsuperConstructor.
As an additional convenience, superConstructor will be accessible\nthrough the constructor.super_ property.
const util = require('util');\nconst EventEmitter = require('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: "${data}"`);\n});\nstream.write('It works!'); // Received data: "It works!"\nES6 example using class and extends
const EventEmitter = require('events');\n\nclass MyStream extends EventEmitter {\n write(data) {\n this.emit('data', data);\n }\n}\n\nconst stream = new MyStream();\n\nstream.on('data', (data) => {\n console.log(`Received data: "${data}"`);\n});\nstream.write('With ES6');\nThe util.inspect() method returns a string representation of object that is\nprimarily useful for debugging. Additional options may be passed that alter\ncertain aspects of the formatted string.
The following example inspects all properties of the util object:
const util = require('util');\n\nconsole.log(util.inspect(util, { showHidden: true, depth: null }));\nValues may supply their own custom inspect(depth, opts) functions, when\ncalled these receive the current depth in the recursive inspection, as well as\nthe options object passed to util.inspect().
The following example highlights the difference with the compact option:
const util = require('util');\n\nconst o = {\n a: [1, 2, [[\n 'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do ' +\n 'eiusmod tempor 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// This will print\n\n// { a:\n// [ 1,\n// 2,\n// [ [ 'Lorem ipsum dolor sit amet, consectetur [...]', // A long line\n// 'test',\n// 'foo' ] ],\n// 4 ],\n// b: Map { 'za' => 1, 'zb' => 'test' } }\n\n// Setting `compact` to false changes the output to be more reader friendly.\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, consectetur ' +\n// 'adipiscing elit, sed do eiusmod tempor ' +\n// 'incididunt ut labore et dolore magna ' +\n// 'aliqua.,\n// 'test',\n// 'foo'\n// ]\n// ],\n// 4\n// ],\n// b: Map {\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.\n// Reducing the `breakLength` will split the "Lorem ipsum" text in smaller\n// chunks.\nPlease note that util.inspect() is a synchronous method that is mainly\nintended as a debugging tool. Some input values can have a significant\nperformance overhead that can block the event loop. Use this function\nwith care and never in a hot code path.
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:
\nnumber - yellowboolean - yellowstring - greendate - magentaregexp - rednull - boldundefined - greyspecial - cyan (only applied to functions at this time)name - (no styling)The predefined color codes are: white, grey, black, blue, cyan,\ngreen, magenta, red and yellow. There are also bold, italic,\nunderline and inverse codes.
Color styling uses ANSI control codes that may not be supported on all\nterminals.
\n" }, { "textRaw": "Custom inspection functions on Objects", "name": "Custom inspection functions on Objects", "type": "misc", "desc": "Objects may also define their own [util.inspect.custom](depth, opts)\n(or the equivalent but deprecated inspect(depth, opts)) function that\nutil.inspect() will invoke and use the result of when inspecting the object:
const util = require('util');\n\nclass Box {\n constructor(value) {\n this.value = value;\n }\n\n [util.inspect.custom](depth, options) {\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 = util.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) functions typically return a string\nbut may return a value of any type that will be formatted accordingly by\nutil.inspect().
const util = require('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' }"\nA Symbol that can be used to declare custom inspect functions, see\nCustom inspection functions on Objects.
\n", "type": "module", "displayName": "util.inspect.custom" }, { "textRaw": "util.inspect.defaultOptions", "name": "util.inspect.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('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.
Takes a function following the common error-first callback style, i.e. taking\na (err, value) => ... callback as the last argument, and returns a version\nthat returns promises.
const util = require('util');\nconst fs = require('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('util');\nconst fs = require('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 the util.promisify.custom symbol one can override the return value of\nutil.promisify():
const util = require('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 (foo, onSuccessCallback, \nonErrorCallback):
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.
A Symbol that can be used to declare custom promisified variants of functions,\nsee Custom promisified functions.
\n", "type": "module", "displayName": "util.promisify.custom" } ] } ], "classes": [ { "textRaw": "Class: util.TextDecoder", "type": "class", "name": "util.TextDecoder", "meta": { "added": [ "v8.3.0" ], "changes": [] }, "desc": "An implementation of the WHATWG Encoding Standard TextDecoder API.
const decoder = new TextDecoder('shift_jis');\nlet string = '';\nlet buffer;\nwhile (buffer = getNextChunkSomehow()) {\n string += decoder.decode(buffer, { stream: true });\n}\nstring += decoder.decode(); // end-of-stream\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.\nWhile a very basic set of encodings is supported even on Node.js builds without\nICU enabled, support for some encodings is provided only when Node.js is built\nwith ICU and using the full ICU data (see Internationalization).
\n", "modules": [ { "textRaw": "Encodings Supported Without ICU", "name": "encodings_supported_without_icu", "desc": "| Encoding | \nAliases | \n
|---|---|
'utf-8' | \n'unicode-1-1-utf-8', 'utf8' | \n
'utf-16le' | \n'utf-16' | \n
| Encoding | \nAliases | \n
|---|---|
'utf-8' | \n'unicode-1-1-utf-8', 'utf8' | \n
'utf-16le' | \n'utf-16' | \n
'utf-16be' | \n
| 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
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 an new TextDecoder instance. The encoding may specify one of the\nsupported encodings or an alias.
Creates an new TextDecoder instance. The encoding may specify one of the\nsupported encodings or an alias.
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');\nUTF-8 encodes the input string and returns a Uint8Array containing the\nencoded bytes.
The encoding supported by the TextEncoder instance. Always set to 'utf-8'.
The following APIs have been deprecated and should no longer be used. Existing\napplications and modules should be updated to find alternative approaches.
\n", "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.", "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().
Deprecated predecessor of console.error.
Deprecated predecessor of console.error.
Internal alias for Array.isArray.
Returns true if the given object is an Array. Otherwise, returns false.
const util = require('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('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('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('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('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\nNote that this 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('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('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('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('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('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. Otherwise, returns false.
const util = require('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('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('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('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('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('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('util');\n\nutil.log('Timestamped message.');\nDeprecated predecessor of console.log.
Deprecated predecessor of console.log.