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<h2>Table of Contents</h2>
<ul>
<li>
<p><span class="stability_2"><a href="#util_util">Util</a></span></p>
<ul>
<li><a href="#util_util_callbackify_original">util.callbackify(original)</a></li>
<li><a href="#util_util_debuglog_section">util.debuglog(section)</a></li>
<li><a href="#util_util_deprecate_fn_msg_code">util.deprecate(fn, msg[, code])</a></li>
<li><a href="#util_util_format_format_args">util.format(format[, ...args])</a></li>
<li><a href="#util_util_formatwithoptions_inspectoptions_format_args">util.formatWithOptions(inspectOptions, format[, ...args])</a></li>
<li><a href="#util_util_getsystemerrorname_err">util.getSystemErrorName(err)</a></li>
<li><a href="#util_util_inherits_constructor_superconstructor">util.inherits(constructor, superConstructor)</a></li>
<li><a href="#util_util_inspect_object_options">util.inspect(object[, options])</a></li>
<li>
<p><a href="#util_util_inspect_object_showhidden_depth_colors">util.inspect(object[, showHidden[, depth[, colors]]])</a></p>
<ul>
<li><a href="#util_customizing_util_inspect_colors">Customizing <code>util.inspect</code> colors</a></li>
<li><a href="#util_custom_inspection_functions_on_objects">Custom inspection functions on Objects</a></li>
<li><a href="#util_util_inspect_custom">util.inspect.custom</a></li>
<li><a href="#util_util_inspect_defaultoptions">util.inspect.defaultOptions</a></li>
</ul>
</li>
<li><a href="#util_util_isdeepstrictequal_val1_val2">util.isDeepStrictEqual(val1, val2)</a></li>
<li>
<p><a href="#util_util_promisify_original">util.promisify(original)</a></p>
<ul>
<li><a href="#util_custom_promisified_functions">Custom promisified functions</a></li>
<li><a href="#util_util_promisify_custom">util.promisify.custom</a></li>
</ul>
</li>
<li>
<p><a href="#util_class_util_textdecoder">Class: util.TextDecoder</a></p>
<ul>
<li>
<p><a href="#util_whatwg_supported_encodings">WHATWG Supported Encodings</a></p>
<ul>
<li><a href="#util_encodings_supported_without_icu">Encodings Supported Without ICU</a></li>
<li><a href="#util_encodings_supported_by_default_with_icu">Encodings Supported by Default (With ICU)</a></li>
<li><a href="#util_encodings_requiring_full_icu_data">Encodings Requiring Full ICU Data</a></li>
</ul>
</li>
<li><a href="#util_new_textdecoder_encoding_options">new TextDecoder([encoding[, options]])</a></li>
<li><a href="#util_textdecoder_decode_input_options">textDecoder.decode([input[, options]])</a></li>
<li><a href="#util_textdecoder_encoding">textDecoder.encoding</a></li>
<li><a href="#util_textdecoder_fatal">textDecoder.fatal</a></li>
<li><a href="#util_textdecoder_ignorebom">textDecoder.ignoreBOM</a></li>
</ul>
</li>
<li>
<p><a href="#util_class_util_textencoder">Class: util.TextEncoder</a></p>
<ul>
<li><a href="#util_textencoder_encode_input">textEncoder.encode([input])</a></li>
<li><a href="#util_textencoder_encoding">textEncoder.encoding</a></li>
</ul>
</li>
<li>
<p><a href="#util_util_types">util.types</a></p>
<ul>
<li><a href="#util_util_types_isanyarraybuffer_value">util.types.isAnyArrayBuffer(value)</a></li>
<li><a href="#util_util_types_isargumentsobject_value">util.types.isArgumentsObject(value)</a></li>
<li><a href="#util_util_types_isarraybuffer_value">util.types.isArrayBuffer(value)</a></li>
<li><a href="#util_util_types_isasyncfunction_value">util.types.isAsyncFunction(value)</a></li>
<li><a href="#util_util_types_isbigint64array_value">util.types.isBigInt64Array(value)</a></li>
<li><a href="#util_util_types_isbiguint64array_value">util.types.isBigUint64Array(value)</a></li>
<li><a href="#util_util_types_isbooleanobject_value">util.types.isBooleanObject(value)</a></li>
<li><a href="#util_util_types_isboxedprimitive_value">util.types.isBoxedPrimitive(value)</a></li>
<li><a href="#util_util_types_isdataview_value">util.types.isDataView(value)</a></li>
<li><a href="#util_util_types_isdate_value">util.types.isDate(value)</a></li>
<li><a href="#util_util_types_isexternal_value">util.types.isExternal(value)</a></li>
<li><a href="#util_util_types_isfloat32array_value">util.types.isFloat32Array(value)</a></li>
<li><a href="#util_util_types_isfloat64array_value">util.types.isFloat64Array(value)</a></li>
<li><a href="#util_util_types_isgeneratorfunction_value">util.types.isGeneratorFunction(value)</a></li>
<li><a href="#util_util_types_isgeneratorobject_value">util.types.isGeneratorObject(value)</a></li>
<li><a href="#util_util_types_isint8array_value">util.types.isInt8Array(value)</a></li>
<li><a href="#util_util_types_isint16array_value">util.types.isInt16Array(value)</a></li>
<li><a href="#util_util_types_isint32array_value">util.types.isInt32Array(value)</a></li>
<li><a href="#util_util_types_ismap_value">util.types.isMap(value)</a></li>
<li><a href="#util_util_types_ismapiterator_value">util.types.isMapIterator(value)</a></li>
<li><a href="#util_util_types_ismodulenamespaceobject_value">util.types.isModuleNamespaceObject(value)</a></li>
<li><a href="#util_util_types_isnativeerror_value">util.types.isNativeError(value)</a></li>
<li><a href="#util_util_types_isnumberobject_value">util.types.isNumberObject(value)</a></li>
<li><a href="#util_util_types_ispromise_value">util.types.isPromise(value)</a></li>
<li><a href="#util_util_types_isproxy_value">util.types.isProxy(value)</a></li>
<li><a href="#util_util_types_isregexp_value">util.types.isRegExp(value)</a></li>
<li><a href="#util_util_types_isset_value">util.types.isSet(value)</a></li>
<li><a href="#util_util_types_issetiterator_value">util.types.isSetIterator(value)</a></li>
<li><a href="#util_util_types_issharedarraybuffer_value">util.types.isSharedArrayBuffer(value)</a></li>
<li><a href="#util_util_types_isstringobject_value">util.types.isStringObject(value)</a></li>
<li><a href="#util_util_types_issymbolobject_value">util.types.isSymbolObject(value)</a></li>
<li><a href="#util_util_types_istypedarray_value">util.types.isTypedArray(value)</a></li>
<li><a href="#util_util_types_isuint8array_value">util.types.isUint8Array(value)</a></li>
<li><a href="#util_util_types_isuint8clampedarray_value">util.types.isUint8ClampedArray(value)</a></li>
<li><a href="#util_util_types_isuint16array_value">util.types.isUint16Array(value)</a></li>
<li><a href="#util_util_types_isuint32array_value">util.types.isUint32Array(value)</a></li>
<li><a href="#util_util_types_isweakmap_value">util.types.isWeakMap(value)</a></li>
<li><a href="#util_util_types_isweakset_value">util.types.isWeakSet(value)</a></li>
<li><a href="#util_util_types_iswebassemblycompiledmodule_value">util.types.isWebAssemblyCompiledModule(value)</a></li>
</ul>
</li>
<li>
<p><a href="#util_deprecated_apis">Deprecated APIs</a></p>
<ul>
<li><span class="stability_0"><a href="#util_util_extend_target_source">util._extend(target, source)</a></span></li>
<li><span class="stability_0"><a href="#util_util_debug_string">util.debug(string)</a></span></li>
<li><span class="stability_0"><a href="#util_util_error_strings">util.error([...strings])</a></span></li>
<li><span class="stability_0"><a href="#util_util_isarray_object">util.isArray(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isboolean_object">util.isBoolean(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isbuffer_object">util.isBuffer(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isdate_object">util.isDate(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_iserror_object">util.isError(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isfunction_object">util.isFunction(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isnull_object">util.isNull(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isnullorundefined_object">util.isNullOrUndefined(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isnumber_object">util.isNumber(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isobject_object">util.isObject(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isprimitive_object">util.isPrimitive(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isregexp_object">util.isRegExp(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isstring_object">util.isString(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_issymbol_object">util.isSymbol(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_isundefined_object">util.isUndefined(object)</a></span></li>
<li><span class="stability_0"><a href="#util_util_log_string">util.log(string)</a></span></li>
<li><span class="stability_0"><a href="#util_util_print_strings">util.print([...strings])</a></span></li>
<li><span class="stability_0"><a href="#util_util_puts_strings">util.puts([...strings])</a></span></li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<div id="apicontent">
<h1>Util<span><a class="mark" href="#util_util" id="util_util">#</a></span></h1>
<p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p>
<p>The <code>util</code> module is primarily designed to support the needs of Node.js' own
internal APIs. However, many of the utilities are useful for application and
module developers as well. It can be accessed using:</p>
<pre><code class="language-js">const util = require('util');
</code></pre>
<h2>util.callbackify(original)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L340">[src]</a><span><a class="mark" href="#util_util_callbackify_original" id="util_util_callbackify_original">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v8.2.0</span>
</div>
<ul>
<li><code>original</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> An <code>async</code> function</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> a callback style function</li>
</ul>
<p>Takes an <code>async</code> function (or a function that returns a <code>Promise</code>) and returns a
function following the error-first callback style, i.e. taking
an <code>(err, value) => ...</code> callback as the last argument. In the callback, the
first argument will be the rejection reason (or <code>null</code> if the <code>Promise</code>
resolved), and the second argument will be the resolved value.</p>
<pre><code class="language-js">const util = require('util');
async function fn() {
return 'hello world';
}
const callbackFunction = util.callbackify(fn);
callbackFunction((err, ret) => {
if (err) throw err;
console.log(ret);
});
</code></pre>
<p>Will print:</p>
<pre><code class="language-txt">hello world
</code></pre>
<p>The callback is executed asynchronously, and will have a limited stack trace.
If the callback throws, the process will emit an <a href="process.html#process_event_uncaughtexception"><code>'uncaughtException'</code></a>
event, and if not handled will exit.</p>
<p>Since <code>null</code> has a special meaning as the first argument to a callback, if a
wrapped function rejects a <code>Promise</code> with a falsy value as a reason, the value
is wrapped in an <code>Error</code> with the original value stored in a field named
<code>reason</code>.</p>
<pre><code class="language-js">function fn() {
return Promise.reject(null);
}
const callbackFunction = util.callbackify(fn);
callbackFunction((err, ret) => {
// When the Promise was rejected with `null` it is wrapped with an Error and
// the original value is stored in `reason`.
err && err.hasOwnProperty('reason') && err.reason === null; // true
});
</code></pre>
<h2>util.debuglog(section)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L181">[src]</a><span><a class="mark" href="#util_util_debuglog_section" id="util_util_debuglog_section">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.11.3</span>
</div>
<ul>
<li><code>section</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A string identifying the portion of the application for
which the <code>debuglog</code> function is being created.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The logging function</li>
</ul>
<p>The <code>util.debuglog()</code> method is used to create a function that conditionally
writes debug messages to <code>stderr</code> based on the existence of the <code>NODE_DEBUG</code>
environment variable. If the <code>section</code> name appears within the value of that
environment variable, then the returned function operates similar to
<a href="console.html#console_console_error_data_args"><code>console.error()</code></a>. If not, then the returned function is a no-op.</p>
<pre><code class="language-js">const util = require('util');
const debuglog = util.debuglog('foo');
debuglog('hello from foo [%d]', 123);
</code></pre>
<p>If this program is run with <code>NODE_DEBUG=foo</code> in the environment, then
it will output something like:</p>
<pre><code class="language-txt">FOO 3245: hello from foo [123]
</code></pre>
<p>where <code>3245</code> is the process id. If it is not run with that
environment variable set, then it will not print anything.</p>
<p>The <code>section</code> supports wildcard also:</p>
<pre><code class="language-js">const util = require('util');
const debuglog = util.debuglog('foo-bar');
debuglog('hi there, it\'s foo-bar [%d]', 2333);
</code></pre>
<p>if it is run with <code>NODE_DEBUG=foo*</code> in the environment, then it will output
something like:</p>
<pre><code class="language-txt">FOO-BAR 3257: hi there, it's foo-bar [2333]
</code></pre>
<p>Multiple comma-separated <code>section</code> names may be specified in the <code>NODE_DEBUG</code>
environment variable: <code>NODE_DEBUG=fs,net,tls</code>.</p>
<h2>util.deprecate(fn, msg[, code])<span><a class="mark" href="#util_util_deprecate_fn_msg_code" id="util_util_deprecate_fn_msg_code">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Deprecation warnings are only emitted once for each code.</p></td></tr>
<tr><td>v0.8.0</td>
<td><p><span>Added in: v0.8.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function that is being deprecated.</li>
<li><code>msg</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A warning message to display when the deprecated function is
invoked.</li>
<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A deprecation code. See the <a href="deprecations.html#deprecations_list_of_deprecated_apis">list of deprecated APIs</a> for a
list of codes.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The deprecated function wrapped to emit a warning.</li>
</ul>
<p>The <code>util.deprecate()</code> method wraps <code>fn</code> (which may be a function or class) in
such a way that it is marked as deprecated.</p>
<pre><code class="language-js">const util = require('util');
exports.obsoleteFunction = util.deprecate(() => {
// Do something here.
}, 'obsoleteFunction() is deprecated. Use newShinyFunction() instead.');
</code></pre>
<p>When called, <code>util.deprecate()</code> will return a function that will emit a
<code>DeprecationWarning</code> using the <a href="process.html#process_event_warning"><code>'warning'</code></a> event. The warning will
be emitted and printed to <code>stderr</code> the first time the returned function is
called. After the warning is emitted, the wrapped function is called without
emitting a warning.</p>
<p>If the same optional <code>code</code> is supplied in multiple calls to <code>util.deprecate()</code>,
the warning will be emitted only once for that <code>code</code>.</p>
<pre><code class="language-js">const util = require('util');
const fn1 = util.deprecate(someFunction, someMessage, 'DEP0001');
const fn2 = util.deprecate(someOtherFunction, someOtherMessage, 'DEP0001');
fn1(); // emits a deprecation warning with code DEP0001
fn2(); // does not emit a deprecation warning because it has the same code
</code></pre>
<p>If either the <code>--no-deprecation</code> or <code>--no-warnings</code> command line flags are
used, or if the <code>process.noDeprecation</code> property is set to <code>true</code> <em>prior</em> to
the first deprecation warning, the <code>util.deprecate()</code> method does nothing.</p>
<p>If the <code>--trace-deprecation</code> or <code>--trace-warnings</code> command line flags are set,
or the <code>process.traceDeprecation</code> property is set to <code>true</code>, a warning and a
stack trace are printed to <code>stderr</code> the first time the deprecated function is
called.</p>
<p>If the <code>--throw-deprecation</code> command line flag is set, or the
<code>process.throwDeprecation</code> property is set to <code>true</code>, then an exception will be
thrown when the deprecated function is called.</p>
<p>The <code>--throw-deprecation</code> command line flag and <code>process.throwDeprecation</code>
property take precedence over <code>--trace-deprecation</code> and
<code>process.traceDeprecation</code>.</p>
<h2>util.format(format[, ...args])<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L71">[src]</a><span><a class="mark" href="#util_util_format_format_args" id="util_util_format_format_args">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.12.0</td>
<td><p>The <code>%d</code> and <code>%i</code> specifiers now support BigInt.</p></td></tr>
<tr><td>v8.4.0</td>
<td><p>The <code>%o</code> and <code>%O</code> specifiers are supported now.</p></td></tr>
<tr><td>v0.5.3</td>
<td><p><span>Added in: v0.5.3</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A <code>printf</code>-like format string.</li>
</ul>
<p>The <code>util.format()</code> method returns a formatted string using the first argument
as a <code>printf</code>-like format.</p>
<p>The first argument is a string containing zero or more <em>placeholder</em> tokens.
Each placeholder token is replaced with the converted value from the
corresponding argument. Supported placeholders are:</p>
<ul>
<li><code>%s</code> - <code>String</code>.</li>
<li><code>%d</code> - <code>Number</code> (integer or floating point value) or <code>BigInt</code>.</li>
<li><code>%i</code> - Integer or <code>BigInt</code>.</li>
<li><code>%f</code> - Floating point value.</li>
<li><code>%j</code> - JSON. Replaced with the string <code>'[Circular]'</code> if the argument
contains circular references.</li>
<li><code>%o</code> - <code>Object</code>. A string representation of an object
with generic JavaScript object formatting.
Similar to <code>util.inspect()</code> with options
<code>{ showHidden: true, showProxy: true }</code>. This will show the full object
including non-enumerable properties and proxies.</li>
<li><code>%O</code> - <code>Object</code>. A string representation of an object with generic JavaScript
object formatting. Similar to <code>util.inspect()</code> without options. This will show
the full object not including non-enumerable properties and proxies.</li>
<li><code>%%</code> - single percent sign (<code>'%'</code>). This does not consume an argument.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The formatted string</li>
</ul>
<p>If the placeholder does not have a corresponding argument, the placeholder is
not replaced.</p>
<pre><code class="language-js">util.format('%s:%s', 'foo');
// Returns: 'foo:%s'
</code></pre>
<p>If there are more arguments passed to the <code>util.format()</code> method than the number
of placeholders, the extra arguments are coerced into strings then concatenated
to the returned string, each delimited by a space. Excessive arguments whose
<code>typeof</code> is <code>'object'</code> or <code>'symbol'</code> (except <code>null</code>) will be transformed by
<code>util.inspect()</code>.</p>
<pre><code class="language-js">util.format('%s:%s', 'foo', 'bar', 'baz'); // 'foo:bar baz'
</code></pre>
<p>If the first argument is not a string then <code>util.format()</code> returns
a string that is the concatenation of all arguments separated by spaces.
Each argument is converted to a string using <code>util.inspect()</code>.</p>
<pre><code class="language-js">util.format(1, 2, 3); // '1 2 3'
</code></pre>
<p>If only one argument is passed to <code>util.format()</code>, it is returned as it is
without any formatting.</p>
<pre><code class="language-js">util.format('%% %s'); // '%% %s'
</code></pre>
<p>Please note that <code>util.format()</code> is a synchronous method that is mainly
intended as a debugging tool. Some input values can have a significant
performance overhead that can block the event loop. Use this function
with care and never in a hot code path.</p>
<h2>util.formatWithOptions(inspectOptions, format[, ...args])<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L75">[src]</a><span><a class="mark" href="#util_util_formatwithoptions_inspectoptions_format_args" id="util_util_formatwithoptions_inspectoptions_format_args">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>inspectOptions</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>This function is identical to <a href="#util_util_format_format_args"><code>util.format()</code></a>, except in that it takes
an <code>inspectOptions</code> argument which specifies options that are passed along to
<a href="#util_util_inspect_object_options"><code>util.inspect()</code></a>.</p>
<pre><code class="language-js">util.formatWithOptions({ colors: true }, 'See object %O', { foo: 42 });
// Returns 'See object { foo: 42 }', where `42` is colored as a number
// when printed to a terminal.
</code></pre>
<h2>util.getSystemErrorName(err)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L367">[src]</a><span><a class="mark" href="#util_util_getsystemerrorname_err" id="util_util_getsystemerrorname_err">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v9.7.0</span>
</div>
<ul>
<li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Returns the string name for a numeric error code that comes from a Node.js API.
The mapping between error codes and error names is platform-dependent.
See <a href="errors.html#errors_common_system_errors">Common System Errors</a> for the names of common errors.</p>
<pre><code class="language-js">fs.access('file/that/does/not/exist', (err) => {
const name = util.getSystemErrorName(err.errno);
console.error(name); // ENOENT
});
</code></pre>
<h2>util.inherits(constructor, superConstructor)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L274">[src]</a><span><a class="mark" href="#util_util_inherits_constructor_superconstructor" id="util_util_inherits_constructor_superconstructor">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v5.0.0</td>
<td><p>The <code>constructor</code> parameter can refer to an ES6 class now.</p></td></tr>
<tr><td>v0.3.0</td>
<td><p><span>Added in: v0.3.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>constructor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>superConstructor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Usage of <code>util.inherits()</code> is discouraged. Please use the ES6 <code>class</code> and
<code>extends</code> keywords to get language level inheritance support. Also note
that the two styles are <a href="https://github.com/nodejs/node/issues/4179">semantically incompatible</a>.</p>
<p>Inherit the prototype methods from one <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/constructor">constructor</a> into another. The
prototype of <code>constructor</code> will be set to a new object created from
<code>superConstructor</code>.</p>
<p>As an additional convenience, <code>superConstructor</code> will be accessible
through the <code>constructor.super_</code> property.</p>
<pre><code class="language-js">const util = require('util');
const EventEmitter = require('events');
function MyStream() {
EventEmitter.call(this);
}
util.inherits(MyStream, EventEmitter);
MyStream.prototype.write = function(data) {
this.emit('data', data);
};
const stream = new MyStream();
console.log(stream instanceof EventEmitter); // true
console.log(MyStream.super_ === EventEmitter); // true
stream.on('data', (data) => {
console.log(`Received data: "${data}"`);
});
stream.write('It works!'); // Received data: "It works!"
</code></pre>
<p>ES6 example using <code>class</code> and <code>extends</code>:</p>
<pre><code class="language-js">const EventEmitter = require('events');
class MyStream extends EventEmitter {
write(data) {
this.emit('data', data);
}
}
const stream = new MyStream();
stream.on('data', (data) => {
console.log(`Received data: "${data}"`);
});
stream.write('With ES6');
</code></pre>
<h2>util.inspect(object[, options])<span><a class="mark" href="#util_util_inspect_object_options" id="util_util_inspect_object_options">#</a></span></h2>
<h2>util.inspect(object[, showHidden[, depth[, colors]]])<span><a class="mark" href="#util_util_inspect_object_showhidden_depth_colors" id="util_util_inspect_object_showhidden_depth_colors">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.12.0</td>
<td><p>The <code>sorted</code> option is supported now.</p></td></tr>
<tr><td>v10.6.0</td>
<td><p>Inspecting linked lists and similar objects is now possible up to the maximum call stack size.</p></td></tr>
<tr><td>v10.0.0</td>
<td><p>The <code>WeakMap</code> and <code>WeakSet</code> entries can now be inspected.</p></td></tr>
<tr><td>v9.9.0</td>
<td><p>The <code>compact</code> option is supported now.</p></td></tr>
<tr><td>v6.6.0</td>
<td><p>Custom inspection functions can now return <code>this</code>.</p></td></tr>
<tr><td>v6.3.0</td>
<td><p>The <code>breakLength</code> option is supported now.</p></td></tr>
<tr><td>v6.1.0</td>
<td><p>The <code>maxArrayLength</code> option is supported now; in particular, long arrays are truncated by default.</p></td></tr>
<tr><td>v6.1.0</td>
<td><p>The <code>showProxy</code> option is supported now.</p></td></tr>
<tr><td>v0.3.0</td>
<td><p><span>Added in: v0.3.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Any JavaScript primitive or <code>Object</code>.</li>
<li>
<p><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></p>
<ul>
<li><code>showHidden</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, the <code>object</code>'s non-enumerable symbols and
properties will be included in the formatted result as well as <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a>
and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> entries. <strong>Default:</strong> <code>false</code>.</li>
<li><code>depth</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Specifies the number of times to recurse while formatting
the <code>object</code>. This is useful for inspecting large complicated objects. To
make it recurse up to the maximum call stack size pass <code>Infinity</code> or <code>null</code>.
<strong>Default:</strong> <code>2</code>.</li>
<li><code>colors</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, the output will be styled with ANSI color
codes. Colors are customizable, see <a href="#util_customizing_util_inspect_colors">Customizing <code>util.inspect</code> colors</a>.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>customInspect</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>false</code>, then custom <code>inspect(depth, opts)</code>
functions will not be called. <strong>Default:</strong> <code>true</code>.</li>
<li><code>showProxy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, then objects and functions that are
<code>Proxy</code> objects will be introspected to show their <code>target</code> and <code>handler</code>
objects. <strong>Default:</strong> <code>false</code>.</li>
<li><code>maxArrayLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Specifies the maximum number of <code>Array</code>,
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> elements to include when
formatting. Set to <code>null</code> or <code>Infinity</code> to show all elements. Set to <code>0</code> or
negative to show no elements. <strong>Default:</strong> <code>100</code>.</li>
<li><code>breakLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The length at which an object's keys are split
across multiple lines. Set to <code>Infinity</code> to format an object as a single
line. <strong>Default:</strong> <code>60</code> for legacy compatibility.</li>
<li><code>compact</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Setting this to <code>false</code> changes the default indentation
to use a line break for each object key instead of lining up multiple
properties in one line. It will also break text that is above the
<code>breakLength</code> size into smaller and better readable chunks and indents
objects the same as arrays. Note that no text will be reduced below 16
characters, no matter the <code>breakLength</code> size. For more information, see the
example below. <strong>Default:</strong> <code>true</code>.</li>
<li><code>sorted</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> If set to <code>true</code> or a function, all properties
of an object and Set and Map entries will be sorted in the returned string.
If set to <code>true</code> the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort">default sort</a> is going to be used. If set to a
function, it is used as a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Parameters">compare function</a>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The representation of passed object</li>
</ul>
<p>The <code>util.inspect()</code> method returns a string representation of <code>object</code> that is
intended for debugging. The output of <code>util.inspect</code> may change at any time
and should not be depended upon programmatically. Additional <code>options</code> may be
passed that alter certain aspects of the formatted string.
<code>util.inspect()</code> will use the constructor's name and/or <code>@@toStringTag</code> to make
an identifiable tag for an inspected value.</p>
<pre><code class="language-js">class Foo {
get [Symbol.toStringTag]() {
return 'bar';
}
}
class Bar {}
const baz = Object.create(null, { [Symbol.toStringTag]: { value: 'foo' } });
util.inspect(new Foo()); // 'Foo [bar] {}'
util.inspect(new Bar()); // 'Bar {}'
util.inspect(baz); // '[foo] {}'
</code></pre>
<p>The following example inspects all properties of the <code>util</code> object:</p>
<pre><code class="language-js">const util = require('util');
console.log(util.inspect(util, { showHidden: true, depth: null }));
</code></pre>
<p>Values may supply their own custom <code>inspect(depth, opts)</code> functions, when
called these receive the current <code>depth</code> in the recursive inspection, as well as
the options object passed to <code>util.inspect()</code>.</p>
<p>The following example highlights the difference with the <code>compact</code> option:</p>
<pre><code class="language-js">const util = require('util');
const o = {
a: [1, 2, [[
'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do ' +
'eiusmod tempor incididunt ut labore et dolore magna aliqua.',
'test',
'foo']], 4],
b: new Map([['za', 1], ['zb', 'test']])
};
console.log(util.inspect(o, { compact: true, depth: 5, breakLength: 80 }));
// This will print
// { a:
// [ 1,
// 2,
// [ [ 'Lorem ipsum dolor sit amet, consectetur [...]', // A long line
// 'test',
// 'foo' ] ],
// 4 ],
// b: Map { 'za' => 1, 'zb' => 'test' } }
// Setting `compact` to false changes the output to be more reader friendly.
console.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 }));
// {
// a: [
// 1,
// 2,
// [
// [
// 'Lorem ipsum dolor sit amet, consectetur ' +
// 'adipiscing elit, sed do eiusmod tempor ' +
// 'incididunt ut labore et dolore magna ' +
// 'aliqua.,
// 'test',
// 'foo'
// ]
// ],
// 4
// ],
// b: Map {
// 'za' => 1,
// 'zb' => 'test'
// }
// }
// Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a
// single line.
// Reducing the `breakLength` will split the "Lorem ipsum" text in smaller
// chunks.
</code></pre>
<p>Using the <code>showHidden</code> option allows to inspect <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a>
entries. If there are more entries than <code>maxArrayLength</code>, there is no guarantee
which entries are displayed. That means retrieving the same <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a>
entries twice might actually result in a different output. Besides this any item
might be collected at any point of time by the garbage collector if there is no
strong reference left to that object. Therefore there is no guarantee to get a
reliable output.</p>
<pre><code class="language-js">const { inspect } = require('util');
const obj = { a: 1 };
const obj2 = { b: 2 };
const weakSet = new WeakSet([obj, obj2]);
console.log(inspect(weakSet, { showHidden: true }));
// WeakSet { { a: 1 }, { b: 2 } }
</code></pre>
<p>The <code>sorted</code> option makes sure the output is identical, no matter of the
properties insertion order:</p>
<pre><code class="language-js">const { inspect } = require('util');
const assert = require('assert');
const o1 = {
b: [2, 3, 1],
a: '`a` comes before `b`',
c: new Set([2, 3, 1])
};
console.log(inspect(o1, { sorted: true }));
// { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set { 1, 2, 3 } }
console.log(inspect(o1, { sorted: (a, b) => b.localeCompare(a) }));
// { c: Set { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' }
const o2 = {
c: new Set([2, 1, 3]),
a: '`a` comes before `b`',
b: [2, 3, 1]
};
assert.strict.equal(
inspect(o1, { sorted: true }),
inspect(o2, { sorted: true })
);
</code></pre>
<p>Please note that <code>util.inspect()</code> is a synchronous method that is mainly
intended as a debugging tool. Some input values can have a significant
performance overhead that can block the event loop. Use this function
with care and never in a hot code path.</p>
<h3>Customizing <code>util.inspect</code> colors<span><a class="mark" href="#util_customizing_util_inspect_colors" id="util_customizing_util_inspect_colors">#</a></span></h3>
<p>Color output (if enabled) of <code>util.inspect</code> is customizable globally
via the <code>util.inspect.styles</code> and <code>util.inspect.colors</code> properties.</p>
<p><code>util.inspect.styles</code> is a map associating a style name to a color from
<code>util.inspect.colors</code>.</p>
<p>The default styles and associated colors are:</p>
<ul>
<li><code>number</code> - <code>yellow</code></li>
<li><code>boolean</code> - <code>yellow</code></li>
<li><code>string</code> - <code>green</code></li>
<li><code>date</code> - <code>magenta</code></li>
<li><code>regexp</code> - <code>red</code></li>
<li><code>null</code> - <code>bold</code></li>
<li><code>undefined</code> - <code>grey</code></li>
<li><code>special</code> - <code>cyan</code> (only applied to functions at this time)</li>
<li><code>name</code> - (no styling)</li>
</ul>
<p>The predefined color codes are: <code>white</code>, <code>grey</code>, <code>black</code>, <code>blue</code>, <code>cyan</code>,
<code>green</code>, <code>magenta</code>, <code>red</code> and <code>yellow</code>. There are also <code>bold</code>, <code>italic</code>,
<code>underline</code> and <code>inverse</code> codes.</p>
<p>Color styling uses ANSI control codes that may not be supported on all
terminals.</p>
<h3>Custom inspection functions on Objects<span><a class="mark" href="#util_custom_inspection_functions_on_objects" id="util_custom_inspection_functions_on_objects">#</a></span></h3>
<p>Objects may also define their own
<a href="#util_util_inspect_custom"><code>[util.inspect.custom](depth, opts)</code></a> (or the equivalent
but deprecated <code>inspect(depth, opts)</code>) function, which <code>util.inspect()</code> will
invoke and use the result of when inspecting the object:</p>
<pre><code class="language-js">const util = require('util');
class Box {
constructor(value) {
this.value = value;
}
[util.inspect.custom](depth, options) {
if (depth < 0) {
return options.stylize('[Box]', 'special');
}
const newOptions = Object.assign({}, options, {
depth: options.depth === null ? null : options.depth - 1
});
// Five space padding because that's the size of "Box< ".
const padding = ' '.repeat(5);
const inner = util.inspect(this.value, newOptions)
.replace(/\n/g, `\n${padding}`);
return `${options.stylize('Box', 'special')}< ${inner} >`;
}
}
const box = new Box(true);
util.inspect(box);
// Returns: "Box< true >"
</code></pre>
<p>Custom <code>[util.inspect.custom](depth, opts)</code> functions typically return a string
but may return a value of any type that will be formatted accordingly by
<code>util.inspect()</code>.</p>
<pre><code class="language-js">const util = require('util');
const obj = { foo: 'this will not show up in the inspect() output' };
obj[util.inspect.custom] = (depth) => {
return { bar: 'baz' };
};
util.inspect(obj);
// Returns: "{ bar: 'baz' }"
</code></pre>
<h3>util.inspect.custom<span><a class="mark" href="#util_util_inspect_custom" id="util_util_inspect_custom">#</a></span></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.12.0</td>
<td><p>This is now defined as a shared symbol.</p></td></tr>
<tr><td>v6.6.0</td>
<td><p><span>Added in: v6.6.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><symbol></a> that can be used to declare custom inspect functions.</li>
</ul>
<p>In addition to being accessible through <code>util.inspect.custom</code>, this
symbol is <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for">registered globally</a> and can be
accessed in any environment as <code>Symbol.for('nodejs.util.inspect.custom')</code>.</p>
<pre><code class="language-js">const inspect = Symbol.for('nodejs.util.inspect.custom');
class Password {
constructor(value) {
this.value = value;
}
toString() {
return 'xxxxxxxx';
}
[inspect]() {
return `Password <${this.toString()}>`;
}
}
const password = new Password('r0sebud');
console.log(password);
// Prints Password <xxxxxxxx>
</code></pre>
<p>See <a href="#util_custom_inspection_functions_on_objects">Custom inspection functions on Objects</a> for more details.</p>
<h3>util.inspect.defaultOptions<span><a class="mark" href="#util_util_inspect_defaultoptions" id="util_util_inspect_defaultoptions">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v6.4.0</span>
</div>
<p>The <code>defaultOptions</code> value allows customization of the default options used by
<code>util.inspect</code>. This is useful for functions like <code>console.log</code> or
<code>util.format</code> which implicitly call into <code>util.inspect</code>. It shall be set to an
object containing one or more valid <a href="#util_util_inspect_object_options"><code>util.inspect()</code></a> options. Setting
option properties directly is also supported.</p>
<pre><code class="language-js">const util = require('util');
const arr = Array(101).fill(0);
console.log(arr); // logs the truncated array
util.inspect.defaultOptions.maxArrayLength = null;
console.log(arr); // logs the full array
</code></pre>
<h2>util.isDeepStrictEqual(val1, val2)<span><a class="mark" href="#util_util_isdeepstrictequal_val1_val2" id="util_util_isdeepstrictequal_val1_val2">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v9.0.0</span>
</div>
<ul>
<li><code>val1</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>val2</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if there is deep strict equality between <code>val1</code> and <code>val2</code>.
Otherwise, returns <code>false</code>.</p>
<p>See <a href="assert.html#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a> for more information about deep strict
equality.</p>
<h2>util.promisify(original)<span><a class="mark" href="#util_util_promisify_original" id="util_util_promisify_original">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<ul>
<li><code>original</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Takes a function following the common error-first callback style, i.e. taking
an <code>(err, value) => ...</code> callback as the last argument, and returns a version
that returns promises.</p>
<pre><code class="language-js">const util = require('util');
const fs = require('fs');
const stat = util.promisify(fs.stat);
stat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});
</code></pre>
<p>Or, equivalently using <code>async function</code>s:</p>
<pre><code class="language-js">const util = require('util');
const fs = require('fs');
const stat = util.promisify(fs.stat);
async function callStat() {
const stats = await stat('.');
console.log(`This directory is owned by ${stats.uid}`);
}
</code></pre>
<p>If there is an <code>original[util.promisify.custom]</code> property present, <code>promisify</code>
will return its value, see <a href="#util_custom_promisified_functions">Custom promisified functions</a>.</p>
<p><code>promisify()</code> assumes that <code>original</code> is a function taking a callback as its
final argument in all cases. If <code>original</code> is not a function, <code>promisify()</code>
will throw an error. If <code>original</code> is a function but its last argument is not
an error-first callback, it will still be passed an error-first
callback as its last argument.</p>
<h3>Custom promisified functions<span><a class="mark" href="#util_custom_promisified_functions" id="util_custom_promisified_functions">#</a></span></h3>
<p>Using the <code>util.promisify.custom</code> symbol one can override the return value of
<a href="#util_util_promisify_original"><code>util.promisify()</code></a>:</p>
<pre><code class="language-js">const util = require('util');
function doSomething(foo, callback) {
// ...
}
doSomething[util.promisify.custom] = (foo) => {
return getPromiseSomehow();
};
const promisified = util.promisify(doSomething);
console.log(promisified === doSomething[util.promisify.custom]);
// prints 'true'
</code></pre>
<p>This can be useful for cases where the original function does not follow the
standard format of taking an error-first callback as the last argument.</p>
<p>For example, with a function that takes in
<code>(foo, onSuccessCallback, onErrorCallback)</code>:</p>
<pre><code class="language-js">doSomething[util.promisify.custom] = (foo) => {
return new Promise((resolve, reject) => {
doSomething(foo, resolve, reject);
});
};
</code></pre>
<p>If <code>promisify.custom</code> is defined but is not a function, <code>promisify()</code> will
throw an error.</p>
<h3>util.promisify.custom<span><a class="mark" href="#util_util_promisify_custom" id="util_util_promisify_custom">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><symbol></a></li>
</ul>
<p>A <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><symbol></a> that can be used to declare custom promisified variants of functions,
see <a href="#util_custom_promisified_functions">Custom promisified functions</a>.</p>
<h2>Class: util.TextDecoder<span><a class="mark" href="#util_class_util_textdecoder" id="util_class_util_textdecoder">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v8.3.0</span>
</div>
<p>An implementation of the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a> <code>TextDecoder</code> API.</p>
<pre><code class="language-js">const decoder = new TextDecoder('shift_jis');
let string = '';
let buffer;
while (buffer = getNextChunkSomehow()) {
string += decoder.decode(buffer, { stream: true });
}
string += decoder.decode(); // end-of-stream
</code></pre>
<h3>WHATWG Supported Encodings<span><a class="mark" href="#util_whatwg_supported_encodings" id="util_whatwg_supported_encodings">#</a></span></h3>
<p>Per the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a>, the encodings supported by the
<code>TextDecoder</code> API are outlined in the tables below. For each encoding,
one or more aliases may be used.</p>
<p>Different Node.js build configurations support different sets of encodings.
While a very basic set of encodings is supported even on Node.js builds without
ICU enabled, support for some encodings is provided only when Node.js is built
with ICU and using the full ICU data (see <a href="intl.html">Internationalization</a>).</p>
<h4>Encodings Supported Without ICU<span><a class="mark" href="#util_encodings_supported_without_icu" id="util_encodings_supported_without_icu">#</a></span></h4>
<table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'utf-8'</code></td><td><code>'unicode-1-1-utf-8'</code>, <code>'utf8'</code></td></tr><tr><td><code>'utf-16le'</code></td><td><code>'utf-16'</code></td></tr></tbody></table>
<h4>Encodings Supported by Default (With ICU)<span><a class="mark" href="#util_encodings_supported_by_default_with_icu" id="util_encodings_supported_by_default_with_icu">#</a></span></h4>
<table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'utf-8'</code></td><td><code>'unicode-1-1-utf-8'</code>, <code>'utf8'</code></td></tr><tr><td><code>'utf-16le'</code></td><td><code>'utf-16'</code></td></tr><tr><td><code>'utf-16be'</code></td><td></td></tr></tbody></table>
<h4>Encodings Requiring Full ICU Data<span><a class="mark" href="#util_encodings_requiring_full_icu_data" id="util_encodings_requiring_full_icu_data">#</a></span></h4>
<table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'ibm866'</code></td><td><code>'866'</code>, <code>'cp866'</code>, <code>'csibm866'</code></td></tr><tr><td><code>'iso-8859-2'</code></td><td><code>'csisolatin2'</code>, <code>'iso-ir-101'</code>, <code>'iso8859-2'</code>, <code>'iso88592'</code>, <code>'iso_8859-2'</code>, <code>'iso_8859-2:1987'</code>, <code>'l2'</code>, <code>'latin2'</code></td></tr><tr><td><code>'iso-8859-3'</code></td><td><code>'csisolatin3'</code>, <code>'iso-ir-109'</code>, <code>'iso8859-3'</code>, <code>'iso88593'</code>, <code>'iso_8859-3'</code>, <code>'iso_8859-3:1988'</code>, <code>'l3'</code>, <code>'latin3'</code></td></tr><tr><td><code>'iso-8859-4'</code></td><td><code>'csisolatin4'</code>, <code>'iso-ir-110'</code>, <code>'iso8859-4'</code>, <code>'iso88594'</code>, <code>'iso_8859-4'</code>, <code>'iso_8859-4:1988'</code>, <code>'l4'</code>, <code>'latin4'</code></td></tr><tr><td><code>'iso-8859-5'</code></td><td><code>'csisolatincyrillic'</code>, <code>'cyrillic'</code>, <code>'iso-ir-144'</code>, <code>'iso8859-5'</code>, <code>'iso88595'</code>, <code>'iso_8859-5'</code>, <code>'iso_8859-5:1988'</code></td></tr><tr><td><code>'iso-8859-6'</code></td><td><code>'arabic'</code>, <code>'asmo-708'</code>, <code>'csiso88596e'</code>, <code>'csiso88596i'</code>, <code>'csisolatinarabic'</code>, <code>'ecma-114'</code>, <code>'iso-8859-6-e'</code>, <code>'iso-8859-6-i'</code>, <code>'iso-ir-127'</code>, <code>'iso8859-6'</code>, <code>'iso88596'</code>, <code>'iso_8859-6'</code>, <code>'iso_8859-6:1987'</code></td></tr><tr><td><code>'iso-8859-7'</code></td><td><code>'csisolatingreek'</code>, <code>'ecma-118'</code>, <code>'elot_928'</code>, <code>'greek'</code>, <code>'greek8'</code>, <code>'iso-ir-126'</code>, <code>'iso8859-7'</code>, <code>'iso88597'</code>, <code>'iso_8859-7'</code>, <code>'iso_8859-7:1987'</code>, <code>'sun_eu_greek'</code></td></tr><tr><td><code>'iso-8859-8'</code></td><td><code>'csiso88598e'</code>, <code>'csisolatinhebrew'</code>, <code>'hebrew'</code>, <code>'iso-8859-8-e'</code>, <code>'iso-ir-138'</code>, <code>'iso8859-8'</code>, <code>'iso88598'</code>, <code>'iso_8859-8'</code>, <code>'iso_8859-8:1988'</code>, <code>'visual'</code></td></tr><tr><td><code>'iso-8859-8-i'</code></td><td><code>'csiso88598i'</code>, <code>'logical'</code></td></tr><tr><td><code>'iso-8859-10'</code></td><td><code>'csisolatin6'</code>, <code>'iso-ir-157'</code>, <code>'iso8859-10'</code>, <code>'iso885910'</code>, <code>'l6'</code>, <code>'latin6'</code></td></tr><tr><td><code>'iso-8859-13'</code></td><td><code>'iso8859-13'</code>, <code>'iso885913'</code></td></tr><tr><td><code>'iso-8859-14'</code></td><td><code>'iso8859-14'</code>, <code>'iso885914'</code></td></tr><tr><td><code>'iso-8859-15'</code></td><td><code>'csisolatin9'</code>, <code>'iso8859-15'</code>, <code>'iso885915'</code>, <code>'iso_8859-15'</code>, <code>'l9'</code></td></tr><tr><td><code>'koi8-r'</code></td><td><code>'cskoi8r'</code>, <code>'koi'</code>, <code>'koi8'</code>, <code>'koi8_r'</code></td></tr><tr><td><code>'koi8-u'</code></td><td><code>'koi8-ru'</code></td></tr><tr><td><code>'macintosh'</code></td><td><code>'csmacintosh'</code>, <code>'mac'</code>, <code>'x-mac-roman'</code></td></tr><tr><td><code>'windows-874'</code></td><td><code>'dos-874'</code>, <code>'iso-8859-11'</code>, <code>'iso8859-11'</code>, <code>'iso885911'</code>, <code>'tis-620'</code></td></tr><tr><td><code>'windows-1250'</code></td><td><code>'cp1250'</code>, <code>'x-cp1250'</code></td></tr><tr><td><code>'windows-1251'</code></td><td><code>'cp1251'</code>, <code>'x-cp1251'</code></td></tr><tr><td><code>'windows-1252'</code></td><td><code>'ansi_x3.4-1968'</code>, <code>'ascii'</code>, <code>'cp1252'</code>, <code>'cp819'</code>, <code>'csisolatin1'</code>, <code>'ibm819'</code>, <code>'iso-8859-1'</code>, <code>'iso-ir-100'</code>, <code>'iso8859-1'</code>, <code>'iso88591'</code>, <code>'iso_8859-1'</code>, <code>'iso_8859-1:1987'</code>, <code>'l1'</code>, <code>'latin1'</code>, <code>'us-ascii'</code>, <code>'x-cp1252'</code></td></tr><tr><td><code>'windows-1253'</code></td><td><code>'cp1253'</code>, <code>'x-cp1253'</code></td></tr><tr><td><code>'windows-1254'</code></td><td><code>'cp1254'</code>, <code>'csisolatin5'</code>, <code>'iso-8859-9'</code>, <code>'iso-ir-148'</code>, <code>'iso8859-9'</code>, <code>'iso88599'</code>, <code>'iso_8859-9'</code>, <code>'iso_8859-9:1989'</code>, <code>'l5'</code>, <code>'latin5'</code>, <code>'x-cp1254'</code></td></tr><tr><td><code>'windows-1255'</code></td><td><code>'cp1255'</code>, <code>'x-cp1255'</code></td></tr><tr><td><code>'windows-1256'</code></td><td><code>'cp1256'</code>, <code>'x-cp1256'</code></td></tr><tr><td><code>'windows-1257'</code></td><td><code>'cp1257'</code>, <code>'x-cp1257'</code></td></tr><tr><td><code>'windows-1258'</code></td><td><code>'cp1258'</code>, <code>'x-cp1258'</code></td></tr><tr><td><code>'x-mac-cyrillic'</code></td><td><code>'x-mac-ukrainian'</code></td></tr><tr><td><code>'gbk'</code></td><td><code>'chinese'</code>, <code>'csgb2312'</code>, <code>'csiso58gb231280'</code>, <code>'gb2312'</code>, <code>'gb_2312'</code>, <code>'gb_2312-80'</code>, <code>'iso-ir-58'</code>, <code>'x-gbk'</code></td></tr><tr><td><code>'gb18030'</code></td><td></td></tr><tr><td><code>'big5'</code></td><td><code>'big5-hkscs'</code>, <code>'cn-big5'</code>, <code>'csbig5'</code>, <code>'x-x-big5'</code></td></tr><tr><td><code>'euc-jp'</code></td><td><code>'cseucpkdfmtjapanese'</code>, <code>'x-euc-jp'</code></td></tr><tr><td><code>'iso-2022-jp'</code></td><td><code>'csiso2022jp'</code></td></tr><tr><td><code>'shift_jis'</code></td><td><code>'csshiftjis'</code>, <code>'ms932'</code>, <code>'ms_kanji'</code>, <code>'shift-jis'</code>, <code>'sjis'</code>, <code>'windows-31j'</code>, <code>'x-sjis'</code></td></tr><tr><td><code>'euc-kr'</code></td><td><code>'cseuckr'</code>, <code>'csksc56011987'</code>, <code>'iso-ir-149'</code>, <code>'korean'</code>, <code>'ks_c_5601-1987'</code>, <code>'ks_c_5601-1989'</code>, <code>'ksc5601'</code>, <code>'ksc_5601'</code>, <code>'windows-949'</code></td></tr></tbody></table>
<p>The <code>'iso-8859-16'</code> encoding listed in the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a>
is not supported.</p>
<h3>new TextDecoder([encoding[, options]])<span><a class="mark" href="#util_new_textdecoder_encoding_options" id="util_new_textdecoder_encoding_options">#</a></span></h3>
<ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Identifies the <code>encoding</code> that this <code>TextDecoder</code> instance
supports. <strong>Default:</strong> <code>'utf-8'</code>.</li>
<li>
<p><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></p>
<ul>
<li><code>fatal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if decoding failures are fatal. This option is only
supported when ICU is enabled (see <a href="intl.html">Internationalization</a>). <strong>Default:</strong>
<code>false</code>.</li>
<li><code>ignoreBOM</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, the <code>TextDecoder</code> will include the byte
order mark in the decoded result. When <code>false</code>, the byte order mark will
be removed from the output. This option is only used when <code>encoding</code> is
<code>'utf-8'</code>, <code>'utf-16be'</code> or <code>'utf-16le'</code>. <strong>Default:</strong> <code>false</code>.</li>
</ul>
</li>
</ul>
<p>Creates an new <code>TextDecoder</code> instance. The <code>encoding</code> may specify one of the
supported encodings or an alias.</p>
<h3>textDecoder.decode([input[, options]])<span><a class="mark" href="#util_textdecoder_decode_input_options" id="util_textdecoder_decode_input_options">#</a></span></h3>
<ul>
<li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> An <code>ArrayBuffer</code>, <code>DataView</code> or
<code>Typed Array</code> instance containing the encoded data.</li>
<li>
<p><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></p>
<ul>
<li><code>stream</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if additional chunks of data are expected.
<strong>Default:</strong> <code>false</code>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Decodes the <code>input</code> and returns a string. If <code>options.stream</code> is <code>true</code>, any
incomplete byte sequences occurring at the end of the <code>input</code> are buffered
internally and emitted after the next call to <code>textDecoder.decode()</code>.</p>
<p>If <code>textDecoder.fatal</code> is <code>true</code>, decoding errors that occur will result in a
<code>TypeError</code> being thrown.</p>
<h3>textDecoder.encoding<span><a class="mark" href="#util_textdecoder_encoding" id="util_textdecoder_encoding">#</a></span></h3>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The encoding supported by the <code>TextDecoder</code> instance.</p>
<h3>textDecoder.fatal<span><a class="mark" href="#util_textdecoder_fatal" id="util_textdecoder_fatal">#</a></span></h3>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>The value will be <code>true</code> if decoding errors result in a <code>TypeError</code> being
thrown.</p>
<h3>textDecoder.ignoreBOM<span><a class="mark" href="#util_textdecoder_ignorebom" id="util_textdecoder_ignorebom">#</a></span></h3>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>The value will be <code>true</code> if the decoding result will include the byte order
mark.</p>
<h2>Class: util.TextEncoder<span><a class="mark" href="#util_class_util_textencoder" id="util_class_util_textencoder">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v8.3.0</span>
</div>
<p>An implementation of the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a> <code>TextEncoder</code> API. All
instances of <code>TextEncoder</code> only support UTF-8 encoding.</p>
<pre><code class="language-js">const encoder = new TextEncoder();
const uint8array = encoder.encode('this is some data');
</code></pre>
<h3>textEncoder.encode([input])<span><a class="mark" href="#util_textencoder_encode_input" id="util_textencoder_encode_input">#</a></span></h3>
<ul>
<li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The text to encode. <strong>Default:</strong> an empty string.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array" class="type"><Uint8Array></a></li>
</ul>
<p>UTF-8 encodes the <code>input</code> string and returns a <code>Uint8Array</code> containing the
encoded bytes.</p>
<h3>textEncoder.encoding<span><a class="mark" href="#util_textencoder_encoding" id="util_textencoder_encoding">#</a></span></h3>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The encoding supported by the <code>TextEncoder</code> instance. Always set to <code>'utf-8'</code>.</p>
<h2>util.types<span><a class="mark" href="#util_util_types" id="util_util_types">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<p><code>util.types</code> provides a number of type checks for different kinds of built-in
objects. Unlike <code>instanceof</code> or <code>Object.prototype.toString.call(value)</code>,
these checks do not inspect properties of the object that are accessible from
JavaScript (like their prototype), and usually have the overhead of
calling into C++.</p>
<p>The result generally does not make any guarantees about what kinds of
properties or behavior a value exposes in JavaScript. They are primarily
useful for addon developers who prefer to do type checking in JavaScript.</p>
<h3>util.types.isAnyArrayBuffer(value)<span><a class="mark" href="#util_util_types_isanyarraybuffer_value" id="util_util_types_isanyarraybuffer_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> or
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instance.</p>
<p>See also <a href="#util_util_types_isarraybuffer_value"><code>util.types.isArrayBuffer()</code></a> and
<a href="#util_util_types_issharedarraybuffer_value"><code>util.types.isSharedArrayBuffer()</code></a>.</p>
<pre><code class="language-js">util.types.isAnyArrayBuffer(new ArrayBuffer()); // Returns true
util.types.isAnyArrayBuffer(new SharedArrayBuffer()); // Returns true
</code></pre>
<h3>util.types.isArgumentsObject(value)<span><a class="mark" href="#util_util_types_isargumentsobject_value" id="util_util_types_isargumentsobject_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an <code>arguments</code> object.</p>
<!-- eslint-disable prefer-rest-params -->
<pre><code class="language-js">function foo() {
util.types.isArgumentsObject(arguments); // Returns true
}
</code></pre>
<h3>util.types.isArrayBuffer(value)<span><a class="mark" href="#util_util_types_isarraybuffer_value" id="util_util_types_isarraybuffer_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> instance.
This does <em>not</em> include <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instances. Usually, it is
desirable to test for both; See <a href="#util_util_types_isanyarraybuffer_value"><code>util.types.isAnyArrayBuffer()</code></a> for that.</p>
<pre><code class="language-js">util.types.isArrayBuffer(new ArrayBuffer()); // Returns true
util.types.isArrayBuffer(new SharedArrayBuffer()); // Returns false
</code></pre>
<h3>util.types.isAsyncFunction(value)<span><a class="mark" href="#util_util_types_isasyncfunction_value" id="util_util_types_isasyncfunction_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function">async function</a>.
Note that this only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.</p>
<pre><code class="language-js">util.types.isAsyncFunction(function foo() {}); // Returns false
util.types.isAsyncFunction(async function foo() {}); // Returns true
</code></pre>
<h3>util.types.isBigInt64Array(value)<span><a class="mark" href="#util_util_types_isbigint64array_value" id="util_util_types_isbigint64array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a <code>BigInt64Array</code> instance.</p>
<pre><code class="language-js">util.types.isBigInt64Array(new BigInt64Array()); // Returns true
util.types.isBigInt64Array(new BigUint64Array()); // Returns false
</code></pre>
<h3>util.types.isBigUint64Array(value)<span><a class="mark" href="#util_util_types_isbiguint64array_value" id="util_util_types_isbiguint64array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a <code>BigUint64Array</code> instance.</p>
<pre><code class="language-js">util.types.isBigUint64Array(new BigInt64Array()); // Returns false
util.types.isBigUint64Array(new BigUint64Array()); // Returns true
</code></pre>
<h3>util.types.isBooleanObject(value)<span><a class="mark" href="#util_util_types_isbooleanobject_value" id="util_util_types_isbooleanobject_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a boolean object, e.g. created
by <code>new Boolean()</code>.</p>
<pre><code class="language-js">util.types.isBooleanObject(false); // Returns false
util.types.isBooleanObject(true); // Returns false
util.types.isBooleanObject(new Boolean(false)); // Returns true
util.types.isBooleanObject(new Boolean(true)); // Returns true
util.types.isBooleanObject(Boolean(false)); // Returns false
util.types.isBooleanObject(Boolean(true)); // Returns false
</code></pre>
<h3>util.types.isBoxedPrimitive(value)<span><a class="mark" href="#util_util_types_isboxedprimitive_value" id="util_util_types_isboxedprimitive_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.11.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is any boxed primitive object, e.g. created
by <code>new Boolean()</code>, <code>new String()</code> or <code>Object(Symbol())</code>.</p>
<p>For example:</p>
<pre><code class="language-js">util.types.isBoxedPrimitive(false); // Returns false
util.types.isBoxedPrimitive(new Boolean(false)); // Returns true
util.types.isBoxedPrimitive(Symbol('foo')); // Returns false
util.types.isBoxedPrimitive(Object(Symbol('foo'))); // Returns true
util.types.isBoxedPrimitive(Object(BigInt(5))); // Returns true
</code></pre>
<h3>util.types.isDataView(value)<span><a class="mark" href="#util_util_types_isdataview_value" id="util_util_types_isdataview_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView"><code>DataView</code></a> instance.</p>
<pre><code class="language-js">const ab = new ArrayBuffer(20);
util.types.isDataView(new DataView(ab)); // Returns true
util.types.isDataView(new Float64Array()); // Returns false
</code></pre>
<p>See also <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView"><code>ArrayBuffer.isView()</code></a>.</p>
<h3>util.types.isDate(value)<span><a class="mark" href="#util_util_types_isdate_value" id="util_util_types_isdate_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date"><code>Date</code></a> instance.</p>
<pre><code class="language-js">util.types.isDate(new Date()); // Returns true
</code></pre>
<h3>util.types.isExternal(value)<span><a class="mark" href="#util_util_types_isexternal_value" id="util_util_types_isexternal_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a native <code>External</code> value.</p>
<h3>util.types.isFloat32Array(value)<span><a class="mark" href="#util_util_types_isfloat32array_value" id="util_util_types_isfloat32array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array"><code>Float32Array</code></a> instance.</p>
<pre><code class="language-js">util.types.isFloat32Array(new ArrayBuffer()); // Returns false
util.types.isFloat32Array(new Float32Array()); // Returns true
util.types.isFloat32Array(new Float64Array()); // Returns false
</code></pre>
<h3>util.types.isFloat64Array(value)<span><a class="mark" href="#util_util_types_isfloat64array_value" id="util_util_types_isfloat64array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array"><code>Float64Array</code></a> instance.</p>
<pre><code class="language-js">util.types.isFloat64Array(new ArrayBuffer()); // Returns false
util.types.isFloat64Array(new Uint8Array()); // Returns false
util.types.isFloat64Array(new Float64Array()); // Returns true
</code></pre>
<h3>util.types.isGeneratorFunction(value)<span><a class="mark" href="#util_util_types_isgeneratorfunction_value" id="util_util_types_isgeneratorfunction_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a generator function.
Note that this only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.</p>
<pre><code class="language-js">util.types.isGeneratorFunction(function foo() {}); // Returns false
util.types.isGeneratorFunction(function* foo() {}); // Returns true
</code></pre>
<h3>util.types.isGeneratorObject(value)<span><a class="mark" href="#util_util_types_isgeneratorobject_value" id="util_util_types_isgeneratorobject_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a generator object as returned from a
built-in generator function.
Note that this only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.</p>
<pre><code class="language-js">function* foo() {}
const generator = foo();
util.types.isGeneratorObject(generator); // Returns true
</code></pre>
<h3>util.types.isInt8Array(value)<span><a class="mark" href="#util_util_types_isint8array_value" id="util_util_types_isint8array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int8Array"><code>Int8Array</code></a> instance.</p>
<pre><code class="language-js">util.types.isInt8Array(new ArrayBuffer()); // Returns false
util.types.isInt8Array(new Int8Array()); // Returns true
util.types.isInt8Array(new Float64Array()); // Returns false
</code></pre>
<h3>util.types.isInt16Array(value)<span><a class="mark" href="#util_util_types_isint16array_value" id="util_util_types_isint16array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int16Array"><code>Int16Array</code></a> instance.</p>
<pre><code class="language-js">util.types.isInt16Array(new ArrayBuffer()); // Returns false
util.types.isInt16Array(new Int16Array()); // Returns true
util.types.isInt16Array(new Float64Array()); // Returns false
</code></pre>
<h3>util.types.isInt32Array(value)<span><a class="mark" href="#util_util_types_isint32array_value" id="util_util_types_isint32array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int32Array"><code>Int32Array</code></a> instance.</p>
<pre><code class="language-js">util.types.isInt32Array(new ArrayBuffer()); // Returns false
util.types.isInt32Array(new Int32Array()); // Returns true
util.types.isInt32Array(new Float64Array()); // Returns false
</code></pre>
<h3>util.types.isMap(value)<span><a class="mark" href="#util_util_types_ismap_value" id="util_util_types_ismap_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> instance.</p>
<pre><code class="language-js">util.types.isMap(new Map()); // Returns true
</code></pre>
<h3>util.types.isMapIterator(value)<span><a class="mark" href="#util_util_types_ismapiterator_value" id="util_util_types_ismapiterator_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an iterator returned for a built-in
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> instance.</p>
<pre><code class="language-js">const map = new Map();
util.types.isMapIterator(map.keys()); // Returns true
util.types.isMapIterator(map.values()); // Returns true
util.types.isMapIterator(map.entries()); // Returns true
util.types.isMapIterator(map[Symbol.iterator]()); // Returns true
</code></pre>
<h3>util.types.isModuleNamespaceObject(value)<span><a class="mark" href="#util_util_types_ismodulenamespaceobject_value" id="util_util_types_ismodulenamespaceobject_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an instance of a <a href="https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects">Module Namespace Object</a>.</p>
<!-- eslint-skip -->
<pre><code class="language-js">import * as ns from './a.js';
util.types.isModuleNamespaceObject(ns); // Returns true
</code></pre>
<h3>util.types.isNativeError(value)<span><a class="mark" href="#util_util_types_isnativeerror_value" id="util_util_types_isnativeerror_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an instance of a built-in <a href="errors.html#errors_class_error"><code>Error</code></a> type.</p>
<pre><code class="language-js">util.types.isNativeError(new Error()); // Returns true
util.types.isNativeError(new TypeError()); // Returns true
util.types.isNativeError(new RangeError()); // Returns true
</code></pre>
<h3>util.types.isNumberObject(value)<span><a class="mark" href="#util_util_types_isnumberobject_value" id="util_util_types_isnumberobject_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a number object, e.g. created
by <code>new Number()</code>.</p>
<pre><code class="language-js">util.types.isNumberObject(0); // Returns false
util.types.isNumberObject(new Number(0)); // Returns true
</code></pre>
<h3>util.types.isPromise(value)<span><a class="mark" href="#util_util_types_ispromise_value" id="util_util_types_ispromise_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise"><code>Promise</code></a>.</p>
<pre><code class="language-js">util.types.isPromise(Promise.resolve(42)); // Returns true
</code></pre>
<h3>util.types.isProxy(value)<span><a class="mark" href="#util_util_types_isproxy_value" id="util_util_types_isproxy_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy"><code>Proxy</code></a> instance.</p>
<pre><code class="language-js">const target = {};
const proxy = new Proxy(target, {});
util.types.isProxy(target); // Returns false
util.types.isProxy(proxy); // Returns true
</code></pre>
<h3>util.types.isRegExp(value)<span><a class="mark" href="#util_util_types_isregexp_value" id="util_util_types_isregexp_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a regular expression object.</p>
<pre><code class="language-js">util.types.isRegExp(/abc/); // Returns true
util.types.isRegExp(new RegExp('abc')); // Returns true
</code></pre>
<h3>util.types.isSet(value)<span><a class="mark" href="#util_util_types_isset_value" id="util_util_types_isset_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> instance.</p>
<pre><code class="language-js">util.types.isSet(new Set()); // Returns true
</code></pre>
<h3>util.types.isSetIterator(value)<span><a class="mark" href="#util_util_types_issetiterator_value" id="util_util_types_issetiterator_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an iterator returned for a built-in
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> instance.</p>
<pre><code class="language-js">const set = new Set();
util.types.isSetIterator(set.keys()); // Returns true
util.types.isSetIterator(set.values()); // Returns true
util.types.isSetIterator(set.entries()); // Returns true
util.types.isSetIterator(set[Symbol.iterator]()); // Returns true
</code></pre>
<h3>util.types.isSharedArrayBuffer(value)<span><a class="mark" href="#util_util_types_issharedarraybuffer_value" id="util_util_types_issharedarraybuffer_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instance.
This does <em>not</em> include <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> instances. Usually, it is
desirable to test for both; See <a href="#util_util_types_isanyarraybuffer_value"><code>util.types.isAnyArrayBuffer()</code></a> for that.</p>
<pre><code class="language-js">util.types.isSharedArrayBuffer(new ArrayBuffer()); // Returns false
util.types.isSharedArrayBuffer(new SharedArrayBuffer()); // Returns true
</code></pre>
<h3>util.types.isStringObject(value)<span><a class="mark" href="#util_util_types_isstringobject_value" id="util_util_types_isstringobject_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a string object, e.g. created
by <code>new String()</code>.</p>
<pre><code class="language-js">util.types.isStringObject('foo'); // Returns false
util.types.isStringObject(new String('foo')); // Returns true
</code></pre>
<h3>util.types.isSymbolObject(value)<span><a class="mark" href="#util_util_types_issymbolobject_value" id="util_util_types_issymbolobject_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a symbol object, created
by calling <code>Object()</code> on a <code>Symbol</code> primitive.</p>
<pre><code class="language-js">const symbol = Symbol('foo');
util.types.isSymbolObject(symbol); // Returns false
util.types.isSymbolObject(Object(symbol)); // Returns true
</code></pre>
<h3>util.types.isTypedArray(value)<span><a class="mark" href="#util_util_types_istypedarray_value" id="util_util_types_istypedarray_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a> instance.</p>
<pre><code class="language-js">util.types.isTypedArray(new ArrayBuffer()); // Returns false
util.types.isTypedArray(new Uint8Array()); // Returns true
util.types.isTypedArray(new Float64Array()); // Returns true
</code></pre>
<p>See also <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView"><code>ArrayBuffer.isView()</code></a>.</p>
<h3>util.types.isUint8Array(value)<span><a class="mark" href="#util_util_types_isuint8array_value" id="util_util_types_isuint8array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array"><code>Uint8Array</code></a> instance.</p>
<pre><code class="language-js">util.types.isUint8Array(new ArrayBuffer()); // Returns false
util.types.isUint8Array(new Uint8Array()); // Returns true
util.types.isUint8Array(new Float64Array()); // Returns false
</code></pre>
<h3>util.types.isUint8ClampedArray(value)<span><a class="mark" href="#util_util_types_isuint8clampedarray_value" id="util_util_types_isuint8clampedarray_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8ClampedArray"><code>Uint8ClampedArray</code></a> instance.</p>
<pre><code class="language-js">util.types.isUint8ClampedArray(new ArrayBuffer()); // Returns false
util.types.isUint8ClampedArray(new Uint8ClampedArray()); // Returns true
util.types.isUint8ClampedArray(new Float64Array()); // Returns false
</code></pre>
<h3>util.types.isUint16Array(value)<span><a class="mark" href="#util_util_types_isuint16array_value" id="util_util_types_isuint16array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint16Array"><code>Uint16Array</code></a> instance.</p>
<pre><code class="language-js">util.types.isUint16Array(new ArrayBuffer()); // Returns false
util.types.isUint16Array(new Uint16Array()); // Returns true
util.types.isUint16Array(new Float64Array()); // Returns false
</code></pre>
<h3>util.types.isUint32Array(value)<span><a class="mark" href="#util_util_types_isuint32array_value" id="util_util_types_isuint32array_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array"><code>Uint32Array</code></a> instance.</p>
<pre><code class="language-js">util.types.isUint32Array(new ArrayBuffer()); // Returns false
util.types.isUint32Array(new Uint32Array()); // Returns true
util.types.isUint32Array(new Float64Array()); // Returns false
</code></pre>
<h3>util.types.isWeakMap(value)<span><a class="mark" href="#util_util_types_isweakmap_value" id="util_util_types_isweakmap_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> instance.</p>
<pre><code class="language-js">util.types.isWeakMap(new WeakMap()); // Returns true
</code></pre>
<h3>util.types.isWeakSet(value)<span><a class="mark" href="#util_util_types_isweakset_value" id="util_util_types_isweakset_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> instance.</p>
<pre><code class="language-js">util.types.isWeakSet(new WeakSet()); // Returns true
</code></pre>
<h3>util.types.isWebAssemblyCompiledModule(value)<span><a class="mark" href="#util_util_types_iswebassemblycompiledmodule_value" id="util_util_types_iswebassemblycompiledmodule_value">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Module"><code>WebAssembly.Module</code></a> instance.</p>
<pre><code class="language-js">const module = new WebAssembly.Module(wasmBuffer);
util.types.isWebAssemblyCompiledModule(module); // Returns true
</code></pre>
<h2>Deprecated APIs<span><a class="mark" href="#util_deprecated_apis" id="util_deprecated_apis">#</a></span></h2>
<p>The following APIs are deprecated and should no longer be used. Existing
applications and modules should be updated to find alternative approaches.</p>
<h3>util._extend(target, source)<span><a class="mark" href="#util_util_extend_target_source" id="util_util_extend_target_source">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.7.5</span><span>Deprecated since: v6.0.0</span>
</div>
<ul>
<li><code>target</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>source</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign"><code>Object.assign()</code></a> instead.</div><p></p>
<p>The <code>util._extend()</code> method was never intended to be used outside of internal
Node.js modules. The community found and used it anyway.</p>
<p>It is deprecated and should not be used in new code. JavaScript comes with very
similar built-in functionality through <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign"><code>Object.assign()</code></a>.</p>
<h3>util.debug(string)<span><a class="mark" href="#util_util_debug_string" id="util_util_debug_string">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span><span>Deprecated since: v0.11.3</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="console.html#console_console_error_data_args"><code>console.error()</code></a> instead.</div><p></p>
<ul>
<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The message to print to <code>stderr</code></li>
</ul>
<p>Deprecated predecessor of <code>console.error</code>.</p>
<h3>util.error([...strings])<span><a class="mark" href="#util_util_error_strings" id="util_util_error_strings">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span><span>Deprecated since: v0.11.3</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="console.html#console_console_error_data_args"><code>console.error()</code></a> instead.</div><p></p>
<ul>
<li><code>...strings</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The message to print to <code>stderr</code></li>
</ul>
<p>Deprecated predecessor of <code>console.error</code>.</p>
<h3>util.isArray(object)<span><a class="mark" href="#util_util_isarray_object" id="util_util_isarray_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray"><code>Array.isArray()</code></a> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Alias for <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray"><code>Array.isArray()</code></a>.</p>
<p>Returns <code>true</code> if the given <code>object</code> is an <code>Array</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isArray([]);
// Returns: true
util.isArray(new Array());
// Returns: true
util.isArray({});
// Returns: false
</code></pre>
<h3>util.isBoolean(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L197">[src]</a><span><a class="mark" href="#util_util_isboolean_object" id="util_util_isboolean_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'boolean'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Boolean</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isBoolean(1);
// Returns: false
util.isBoolean(0);
// Returns: false
util.isBoolean(false);
// Returns: true
</code></pre>
<h3>util.isBuffer(object)<span><a class="mark" href="#util_util_isbuffer_object" id="util_util_isbuffer_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="buffer.html#buffer_class_method_buffer_isbuffer_obj"><code>Buffer.isBuffer()</code></a> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Buffer</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isBuffer({ length: 0 });
// Returns: false
util.isBuffer([]);
// Returns: false
util.isBuffer(Buffer.from('hello world'));
// Returns: true
</code></pre>
<h3>util.isDate(object)<span><a class="mark" href="#util_util_isdate_object" id="util_util_isdate_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="#util_util_types_isdate_value"><code>util.types.isDate()</code></a> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Date</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isDate(new Date());
// Returns: true
util.isDate(Date());
// false (without 'new' returns a String)
util.isDate({});
// Returns: false
</code></pre>
<h3>util.isError(object)<span><a class="mark" href="#util_util_iserror_object" id="util_util_iserror_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="#util_util_types_isnativeerror_value"><code>util.types.isNativeError()</code></a> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is an <a href="errors.html#errors_class_error"><code>Error</code></a>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isError(new Error());
// Returns: true
util.isError(new TypeError());
// Returns: true
util.isError({ name: 'Error', message: 'an error occurred' });
// Returns: false
</code></pre>
<p>Note that this method relies on <code>Object.prototype.toString()</code> behavior. It is
possible to obtain an incorrect result when the <code>object</code> argument manipulates
<code>@@toStringTag</code>.</p>
<pre><code class="language-js">const util = require('util');
const obj = { name: 'Error', message: 'an error occurred' };
util.isError(obj);
// Returns: false
obj[Symbol.toStringTag] = 'Error';
util.isError(obj);
// Returns: true
</code></pre>
<h3>util.isFunction(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L229">[src]</a><span><a class="mark" href="#util_util_isfunction_object" id="util_util_isfunction_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'function'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Function</code>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
function Foo() {}
const Bar = () => {};
util.isFunction({});
// Returns: false
util.isFunction(Foo);
// Returns: true
util.isFunction(Bar);
// Returns: true
</code></pre>
<h3>util.isNull(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L201">[src]</a><span><a class="mark" href="#util_util_isnull_object" id="util_util_isnull_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>value === null</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is strictly <code>null</code>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isNull(0);
// Returns: false
util.isNull(undefined);
// Returns: false
util.isNull(null);
// Returns: true
</code></pre>
<h3>util.isNullOrUndefined(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L205">[src]</a><span><a class="mark" href="#util_util_isnullorundefined_object" id="util_util_isnullorundefined_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use
<code>value === undefined || value === null</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is <code>null</code> or <code>undefined</code>. Otherwise,
returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isNullOrUndefined(0);
// Returns: false
util.isNullOrUndefined(undefined);
// Returns: true
util.isNullOrUndefined(null);
// Returns: true
</code></pre>
<h3>util.isNumber(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L209">[src]</a><span><a class="mark" href="#util_util_isnumber_object" id="util_util_isnumber_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'number'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Number</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isNumber(false);
// Returns: false
util.isNumber(Infinity);
// Returns: true
util.isNumber(0);
// Returns: true
util.isNumber(NaN);
// Returns: true
</code></pre>
<h3>util.isObject(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L225">[src]</a><span><a class="mark" href="#util_util_isobject_object" id="util_util_isobject_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated:
Use <code>value !== null && typeof value === 'object'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is strictly an <code>Object</code> <strong>and</strong> not a
<code>Function</code> (even though functions are objects in JavaScript).
Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isObject(5);
// Returns: false
util.isObject(null);
// Returns: false
util.isObject({});
// Returns: true
util.isObject(() => {});
// Returns: false
</code></pre>
<h3>util.isPrimitive(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L233">[src]</a><span><a class="mark" href="#util_util_isprimitive_object" id="util_util_isprimitive_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use
<code>(typeof value !== 'object' && typeof value !== 'function') || value === null</code>
instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a primitive type. Otherwise, returns
<code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isPrimitive(5);
// Returns: true
util.isPrimitive('foo');
// Returns: true
util.isPrimitive(false);
// Returns: true
util.isPrimitive(null);
// Returns: true
util.isPrimitive(undefined);
// Returns: true
util.isPrimitive({});
// Returns: false
util.isPrimitive(() => {});
// Returns: false
util.isPrimitive(/^$/);
// Returns: false
util.isPrimitive(new Date());
// Returns: false
</code></pre>
<h3>util.isRegExp(object)<span><a class="mark" href="#util_util_isregexp_object" id="util_util_isregexp_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>RegExp</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isRegExp(/some regexp/);
// Returns: true
util.isRegExp(new RegExp('another regexp'));
// Returns: true
util.isRegExp({});
// Returns: false
</code></pre>
<h3>util.isString(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L213">[src]</a><span><a class="mark" href="#util_util_isstring_object" id="util_util_isstring_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'string'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>string</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isString('');
// Returns: true
util.isString('foo');
// Returns: true
util.isString(String('foo'));
// Returns: true
util.isString(5);
// Returns: false
</code></pre>
<h3>util.isSymbol(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L217">[src]</a><span><a class="mark" href="#util_util_issymbol_object" id="util_util_issymbol_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'symbol'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Symbol</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
util.isSymbol(5);
// Returns: false
util.isSymbol('foo');
// Returns: false
util.isSymbol(Symbol('foo'));
// Returns: true
</code></pre>
<h3>util.isUndefined(object)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L221">[src]</a><span><a class="mark" href="#util_util_isundefined_object" id="util_util_isundefined_object">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>value === undefined</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is <code>undefined</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js">const util = require('util');
const foo = undefined;
util.isUndefined(5);
// Returns: false
util.isUndefined(foo);
// Returns: true
util.isUndefined(null);
// Returns: false
</code></pre>
<h3>util.log(string)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/util.js#L255">[src]</a><span><a class="mark" href="#util_util_log_string" id="util_util_log_string">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span><span>Deprecated since: v6.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use a third party module instead.</div><p></p>
<ul>
<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The <code>util.log()</code> method prints the given <code>string</code> to <code>stdout</code> with an included
timestamp.</p>
<pre><code class="language-js">const util = require('util');
util.log('Timestamped message.');
</code></pre>
<h3>util.print([...strings])<span><a class="mark" href="#util_util_print_strings" id="util_util_print_strings">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span><span>Deprecated since: v0.11.3</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="console.html#console_console_log_data_args"><code>console.log()</code></a> instead.</div><p></p>
<p>Deprecated predecessor of <code>console.log</code>.</p>
<h3>util.puts([...strings])<span><a class="mark" href="#util_util_puts_strings" id="util_util_puts_strings">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.3.0</span><span>Deprecated since: v0.11.3</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="console.html#console_console_log_data_args"><code>console.log()</code></a> instead.</div><p></p>
<p>Deprecated predecessor of <code>console.log</code>.</p>
</div>
</div>
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