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 โ€œDetermining with absolute accuracy whether or not a JavaScript object is an arrayโ€ 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

DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
isArrayChrome Full support 5Edge Full support 12Firefox Full support 4IE Full support 9Opera Full support 10.5Safari Full support 5WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 14Safari iOS Full support 5Samsung Internet Android Full support 1.0nodejs Full support 0.1.100

Legend

Full support
Full support

See also