Node.js util/types module | API Reference | Bun

Returns true if the value is a built-in ArrayBuffer or SharedArrayBuffer instance.

See also util.types.isArrayBuffer() and util.types.isSharedArrayBuffer().

util.types.isAnyArrayBuffer(new ArrayBuffer()); // Returns true
util.types.isAnyArrayBuffer(new SharedArrayBuffer()); // Returns true

Returns true if the value is an arguments object.

function foo() {
util.types.isArgumentsObject(arguments); // Returns true
}

Returns true if the value is a built-in ArrayBuffer instance. This does not include SharedArrayBuffer instances. Usually, it is desirable to test for both; See util.types.isAnyArrayBuffer() for that.

util.types.isArrayBuffer(new ArrayBuffer()); // Returns true
util.types.isArrayBuffer(new SharedArrayBuffer()); // Returns false

Returns true if the value is an instance of one of the ArrayBuffer views, such as typed array objects or DataView. Equivalent to ArrayBuffer.isView().

util.types.isArrayBufferView(new Int8Array()); // true
util.types.isArrayBufferView(Buffer.from('hello world')); // true
util.types.isArrayBufferView(new DataView(new ArrayBuffer(16))); // true
util.types.isArrayBufferView(new ArrayBuffer()); // false

Returns true if the value is an async function. 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.

util.types.isAsyncFunction(function foo() {}); // Returns false
util.types.isAsyncFunction(async function foo() {}); // Returns true

Returns true if the value is a BigInt64Array instance.

util.types.isBigInt64Array(new BigInt64Array()); // Returns true
util.types.isBigInt64Array(new BigUint64Array()); // Returns false

Returns true if the value is a BigInt object, e.g. created by Object(BigInt(123)).

util.types.isBigIntObject(Object(BigInt(123))); // Returns true
util.types.isBigIntObject(BigInt(123)); // Returns false
util.types.isBigIntObject(123); // Returns false

Returns true if the value is a BigUint64Array instance.

util.types.isBigUint64Array(new BigInt64Array()); // Returns false
util.types.isBigUint64Array(new BigUint64Array()); // Returns true

Returns true if the value is a boolean object, e.g. created by new Boolean().

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

Returns true if the value is any boxed primitive object, e.g. created by new Boolean(), new String() or Object(Symbol()).

For example:

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

Returns true if value is a CryptoKey, false otherwise.

Returns true if the value is a built-in DataView instance.

const ab = new ArrayBuffer(20);
util.types.isDataView(new DataView(ab)); // Returns true
util.types.isDataView(new Float64Array()); // Returns false

See also ArrayBuffer.isView().

Returns true if the value is a built-in Date instance.

util.types.isDate(new Date()); // Returns true

Returns true if the value is a native External value.

A native External value is a special type of object that contains a raw C++ pointer (void*) for access from native code, and has no other properties. Such objects are created either by Node.js internals or native addons. In JavaScript, they are frozen objects with a null prototype.

#include js_native_api.h>
#include stdlib.h>
napi_value result;
static napi_value MyNapi(napi_env env, napi_callback_info info) {
int* raw = (int*) malloc(1024);
napi_status status = napi_create_external(env, (void*) raw, NULL, NULL, &result);
if (status != napi_ok) {
napi_throw_error(env, NULL, "napi_create_external failed");
return NULL;
}
return result;
}
...
DECLARE_NAPI_PROPERTY("myNapi", MyNapi)
...

import native from 'napi_addon.node';
import { types } from 'node:util';

const data = native.myNapi();
types.isExternal(data); // returns true
types.isExternal(0); // returns false
types.isExternal(new String('foo')); // returns false

For further information on napi_create_external, refer to napi_create_external().

Returns true if the value is a built-in Float16Array instance.

util.types.isFloat16Array(new ArrayBuffer()); // Returns false
util.types.isFloat16Array(new Float16Array()); // Returns true
util.types.isFloat16Array(new Float32Array()); // Returns false

Returns true if the value is a built-in Float32Array instance.

util.types.isFloat32Array(new ArrayBuffer()); // Returns false
util.types.isFloat32Array(new Float32Array()); // Returns true
util.types.isFloat32Array(new Float64Array()); // Returns false

Returns true if the value is a built-in Float64Array instance.

util.types.isFloat64Array(new ArrayBuffer()); // Returns false
util.types.isFloat64Array(new Uint8Array()); // Returns false
util.types.isFloat64Array(new Float64Array()); // Returns true

Returns true if the value is a generator function. 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.

util.types.isGeneratorFunction(function foo() {}); // Returns false
util.types.isGeneratorFunction(function* foo() {}); // Returns true

Returns true if the value is a generator object as returned from a built-in generator function. 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.

function* foo() {}
const generator = foo();
util.types.isGeneratorObject(generator); // Returns true

Returns true if the value is a built-in Int16Array instance.

util.types.isInt16Array(new ArrayBuffer()); // Returns false
util.types.isInt16Array(new Int16Array()); // Returns true
util.types.isInt16Array(new Float64Array()); // Returns false

Returns true if the value is a built-in Int32Array instance.

util.types.isInt32Array(new ArrayBuffer()); // Returns false
util.types.isInt32Array(new Int32Array()); // Returns true
util.types.isInt32Array(new Float64Array()); // Returns false

Returns true if the value is a built-in Int8Array instance.

util.types.isInt8Array(new ArrayBuffer()); // Returns false
util.types.isInt8Array(new Int8Array()); // Returns true
util.types.isInt8Array(new Float64Array()); // Returns false

Returns true if value is a KeyObject, false otherwise.

Returns true if the value is a built-in Map instance.

util.types.isMap(new Map()); // Returns true

Returns true if the value is an iterator returned for a built-in Map instance.

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

Returns true if the value is an instance of a Module Namespace Object.

import * as ns from './a.js';

util.types.isModuleNamespaceObject(ns); // Returns true

Returns true if the value is a number object, e.g. created by new Number().

util.types.isNumberObject(0); // Returns false
util.types.isNumberObject(new Number(0)); // Returns true

Returns true if the value is a built-in Promise.

util.types.isPromise(Promise.resolve(42)); // Returns true

Returns true if the value is a Proxy instance.

const target = {};
const proxy = new Proxy(target, {});
util.types.isProxy(target); // Returns false
util.types.isProxy(proxy); // Returns true

Returns true if the value is a regular expression object.

util.types.isRegExp(/abc/); // Returns true
util.types.isRegExp(new RegExp('abc')); // Returns true

Returns true if the value is a built-in Set instance.

util.types.isSet(new Set()); // Returns true

Returns true if the value is an iterator returned for a built-in Set instance.

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

Returns true if the value is a built-in SharedArrayBuffer instance. This does not include ArrayBuffer instances. Usually, it is desirable to test for both; See util.types.isAnyArrayBuffer() for that.

util.types.isSharedArrayBuffer(new ArrayBuffer()); // Returns false
util.types.isSharedArrayBuffer(new SharedArrayBuffer()); // Returns true

Returns true if the value is a string object, e.g. created by new String().

util.types.isStringObject('foo'); // Returns false
util.types.isStringObject(new String('foo')); // Returns true

Returns true if the value is a symbol object, created by calling Object() on a Symbol primitive.

const symbol = Symbol('foo');
util.types.isSymbolObject(symbol); // Returns false
util.types.isSymbolObject(Object(symbol)); // Returns true

Returns true if the value is a built-in TypedArray instance.

util.types.isTypedArray(new ArrayBuffer()); // Returns false
util.types.isTypedArray(new Uint8Array()); // Returns true
util.types.isTypedArray(new Float64Array()); // Returns true

See also ArrayBuffer.isView().

Returns true if the value is a built-in Uint16Array instance.

util.types.isUint16Array(new ArrayBuffer()); // Returns false
util.types.isUint16Array(new Uint16Array()); // Returns true
util.types.isUint16Array(new Float64Array()); // Returns false

Returns true if the value is a built-in Uint32Array instance.

util.types.isUint32Array(new ArrayBuffer()); // Returns false
util.types.isUint32Array(new Uint32Array()); // Returns true
util.types.isUint32Array(new Float64Array()); // Returns false

Returns true if the value is a built-in Uint8Array instance.

util.types.isUint8Array(new ArrayBuffer()); // Returns false
util.types.isUint8Array(new Uint8Array()); // Returns true
util.types.isUint8Array(new Float64Array()); // Returns false

Returns true if the value is a built-in Uint8ClampedArray instance.

util.types.isUint8ClampedArray(new ArrayBuffer()); // Returns false
util.types.isUint8ClampedArray(new Uint8ClampedArray()); // Returns true
util.types.isUint8ClampedArray(new Float64Array()); // Returns false

Returns true if the value is a built-in WeakMap instance.

util.types.isWeakMap(new WeakMap()); // Returns true

Returns true if the value is a built-in WeakSet instance.

util.types.isWeakSet(new WeakSet()); // Returns true