Array.prototype.concat()

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.

Syntax

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

Parameters

valueN

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

Return value

A new Array instance.

Description

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.

Examples

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]);

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

Specifications

Browser compatibility

See also

• push / pop — add/remove elements from the end of the array
• unshift / shift — add/remove elements from the beginning of the array
• splice — add/remove elements from the specified location of the array
• String.prototype.concat()
• Symbol.isConcatSpreadable – control flattening.