Array.isArray() - JavaScript

Array.prototype.entries()
Array.prototype.find()
Array.prototype.flat()
Array.prototype.indexOf()
Array.prototype.map()
Array.prototype.reduceRight()
Array.prototype.some()
Array.prototype.toReversed()
Array.prototype.unshift()
Array: length
Function.prototype.bind()
Function: displayName Non-standard
Function.prototype.arguments Non-standard Deprecated
Function.prototype.caller Non-standard Deprecated

Instance methods

Object.prototype.__defineGetter__() Deprecated
Object.prototype.__defineSetter__() Deprecated
Object.prototype.__lookupGetter__() Deprecated
Object.prototype.__lookupSetter__() Deprecated
Object.prototype.toLocaleString()
Object.prototype.__proto__ Deprecated
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 in operator, for a private property 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