Array.isArray()

BaselineWidely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

TheArray.isArray() static method determines whether the passed value is anArray.

Try it

console.log(Array.isArray([1, 3, 5]));// Expected output: trueconsole.log(Array.isArray("[]"));// Expected output: falseconsole.log(Array.isArray(new Array(5)));// Expected output: trueconsole.log(Array.isArray(new Int16Array([15, 33])));// Expected output: false

Syntax

Array.isArray(value)

Parameters

value: The value to be checked.

Return value

true ifvalue is anArray; otherwise,false.false is always returned ifvalue is aTypedArray instance.

Description

Array.isArray() checks if the passed value is anArray. It performs abranded check, similar to thein operator, for a private field initialized by theArray() constructor.

It is a more robust alternative toinstanceof Array because it avoids false positives and false negatives:

Array.isArray() rejects values that aren't actualArray instances, even if they haveArray.prototype in their prototype chain —instanceof Array would accept these as it does check the prototype chain.
Array.isArray() acceptsArray objects constructed in another realm —instanceof Array returnsfalse for these because the identity of theArray constructor is different across realms.

See the article"Determining with absolute accuracy whether or not a JavaScript object is an array" for more details.

Examples

Using Array.isArray()

// all following calls return trueArray.isArray([]);Array.isArray([1]);Array.isArray(new Array());Array.isArray(new Array("a", "b", "c", "d"));Array.isArray(new Array(3));// Little known fact: Array.prototype itself is an array:Array.isArray(Array.prototype);// all following calls return falseArray.isArray();Array.isArray({});Array.isArray(null);Array.isArray(undefined);Array.isArray(17);Array.isArray("Array");Array.isArray(true);Array.isArray(false);Array.isArray(new Uint8Array(32));// This is not an array, because it was not created using the// array literal syntax or the Array constructorArray.isArray({ __proto__: Array.prototype });

instanceof vs. Array.isArray()

When checking forArray instance,Array.isArray() is preferred overinstanceof because it works across realms.

const iframe = document.createElement("iframe");document.body.appendChild(iframe);const xArray = window.frames[window.frames.length - 1].Array;const arr = new xArray(1, 2, 3); // [1, 2, 3]// Correctly checking for ArrayArray.isArray(arr); // true// The prototype of arr is xArray.prototype, which is a// different object from Array.prototypearr instanceof Array; // false