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

Browser compatibility

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See also