Array.isArray

The Array.isArray() 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(obj)

Parameters

obj

The object to be checked.

Return value

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

Description

If the object 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.

Examples

// all following calls return true
Array.isArray([]);
Array.isArray([1]);
Array.isArray(new Array());
// 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({ __proto__: Array.prototype });

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]';
  };
}

Specifications

Specification	Status	Comment
ECMAScript 5.1 (ECMA-262) The definition of 'Array.isArray' in that specification.	Standard	Initial definition. Implemented in JavaScript 1.8.5.
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Array.isArray' in that specification.	Standard
ECMAScript 2017 Draft (ECMA-262) The definition of 'Array.isArray' in that specification.	Draft

Browser compatibility

See also

• Array