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Array.isArray()

Baseline Widely available

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

The Array.isArray() static method determines whether the passed value is an Array.

Try it

console.log(Array.isArray([1, 3, 5]));
// Expected output: true

console.log(Array.isArray("[]"));
// Expected output: false

console.log(Array.isArray(new Array(5)));
// Expected output: true

console.log(Array.isArray(new Int16Array([15, 33])));
// Expected output: false

Syntax

Array.isArray(value)

Parameters

value: The value to be checked.

Return value

true if value is an Array; otherwise, false. false is always returned if value is a TypedArray instance.

Description

Array.isArray() checks if the passed value is an Array. It performs a branded check, similar to the in operator, for a private field initialized by the Array() constructor.

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

Array.isArray() rejects values that aren't actual Array instances, even if they have Array.prototype in their prototype chain — instanceof Array would accept these as it does check the prototype chain.
Array.isArray() accepts Array objects constructed in another realm — instanceof Array returns false for these because the identity of the Array 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 true
Array.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 false
Array.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 constructor
Array.isArray({ __proto__: Array.prototype });

instanceof vs. Array.isArray()

When checking for Array instance, Array.isArray() is preferred over instanceof 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 Array
Array.isArray(arr); // true
// The prototype of arr is xArray.prototype, which is a
// different object from Array.prototype
arr instanceof Array; // false

Specifications

Specification
ECMAScript® 2026 Language Specification> # sec-array.isarray>

Browser compatibility

	Desktop					Mobile							Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS	Bun	Deno	Node.js
`isArray`	4	12	4	10.5	5	18	4	14	5	1.0	4.4	5	1.0.0	1.0	0.10.0