Web/JavaScript/Reference/Global objects/Array/isArray

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

Array.isArray([1, 2, 3]);  // true
Array.isArray({foo: 123}); // false
Array.isArray('foobar');   // false
Array.isArray(undefined);  // false

Syntax

Array.isArray(value)

Parameters

value

The value to be checked.

Return value

true if the value is an Array; otherwise, false.

Description

If the value is an Array, true is returned; otherwise, false is. 

See the article “Determining with absolute accuracy whether or not a JavaScript object is an array” for more details. Given a TypedArray instance, false is always returned.

Polyfill

Running the following code before any other code will create Array.isArray() if it's not natively available.

if (!Array.isArray) {
  Array.isArray = function(arg) {
    return Object.prototype.toString.call(arg) === '[object Array]';
  };
}

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));
Array.isArray({ __proto__: Array.prototype });

instanceof vs isArray

When checking for Array instance, Array.isArray is preferred over instanceof because it works through iframes.

var iframe = document.createElement('iframe');
document.body.appendChild(iframe);
xArray = window.frames[window.frames.length-1].Array;
var arr = new xArray(1,2,3); // [1,2,3]

// Correctly checking for Array
Array.isArray(arr);  // true
// Considered harmful, because doesn't work through iframes
arr instanceof Array; // false

Specifications

Specification

ECMAScript (ECMA-262)The definition of 'Array.isArray' in that specification.

Browser compatibility

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
isArray	Chrome Full support 5	Edge Full support 12	Firefox Full support 4	IE Full support 9	Opera Full support 10.5	Safari Full support 5	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 14	Safari iOS Full support 5	Samsung Internet Android Full support 1.0	nodejs Full support 0.1.100

Legend

Full support  

Full support

See also

• Array

Array.isArray() by Mozilla Contributors is licensed under CC-BY-SA 2.5.