The concat() method returns a new array comprised of the array on which it is called joined with the array(s) and/or value(s) provided as arguments.


var <var>new_array</var> = <var>old_array</var>.concat(<var>value1</var>[, <var>value2</var>[, ...[, <var>valueN</var>]]])


Arrays and/or values to concatenate into a new array. See the description below for details.

Return value

A new Array instance.


concat creates a new array consisting of the elements in the object on which it is called, followed in order by, for each argument, the elements of that argument (if the argument is an array) or the argument itself (if the argument is not an array).

concat does not alter this or any of the arrays provided as arguments but instead returns a shallow copy that contains copies of the same elements combined from the original arrays. Elements of the original arrays are copied into the new array as follows:

  • Object references (and not the actual object): concat copies object references into the new array. Both the original and new array refer to the same object. That is, if a referenced object is modified, the changes are visible to both the new and original arrays.
  • Strings, numbers and booleans (not String, Number, and Boolean objects): concat copies the values of strings and numbers into the new array.

Note: Concatenating array(s)/value(s) will leave the originals untouched. Furthermore, any operation on the new array(only if the element is not object reference) will have no effect on the original arrays, and vice versa.


Concatenating two arrays

The following code concatenates two arrays:

var alpha = ['a', 'b', 'c'],
    numeric = [1, 2, 3];

var alphaNumeric = alpha.concat(numeric);

console.log(alphaNumeric); // Result: ['a', 'b', 'c', 1, 2, 3]

Concatenating three arrays

The following code concatenates three arrays:

var num1 = [1, 2, 3],
    num2 = [4, 5, 6],
    num3 = [7, 8, 9];

var nums = num1.concat(num2, num3);

console.log(nums); // Result: [1, 2, 3, 4, 5, 6, 7, 8, 9]

Concatenating values to an array

The following code concatenates three values to an array:

var alpha = ['a', 'b', 'c'];

var alphaNumeric = alpha.concat(1, [2, 3]);

// Result: ['a', 'b', 'c', 1, 2, 3]


Specification Status Comment
ECMAScript 3rd Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.2.
ECMAScript 5.1 (ECMA-262)
The definition of 'Array.prototype.concat' in that specification.
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Array.prototype.concat' in that specification.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Array.prototype.concat' in that specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 1.0 1.0 (1.7 or earlier) 5.5 (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

Array JavaScript Method Prototype