JavaScript Array concat() Method

The concat() method concatenates (joins) two or more arrays. It returns a new array, containing the joined arrays. This method is useful for combining arrays without modifying the originals.

Syntax:

let newArray1 = oldArray.concat()
let newArray2 = oldArray.concat(value0)
let newArray3 = oldArray.concat(value0,value1)
.......
.......
let newArray = oldArray.concat(value1 , [ value2, [ ...,[ valueN]]])

Parameters:

The parameters of this method are the arrays or the values that need to be added to the given array. The number of arguments to this method depends upon the number of arrays or values to be merged.

Return value:

This method returns a newly created array that is created after merging all the arrays passed to the method as arguments. 

Example 1: Below is an example of the Array concat() method to join three arrays.

// JavaScript code for concat() method
function func() {
    let num1 = [11, 12, 13],
        num2 = [14, 15, 16],
        num3 = [17, 18, 19];
    console.log(num1.concat(num2, num3));
}
func();

[
  11, 12, 13, 14, 15,
  16, 17, 18, 19
]

Example 2: In this example, the method concat() concatenates all the arguments passed to the method with the given array into one array which it returns as the answer.

// JavaScript code for concat() method
function func() {
    let alpha = ["a", "b", "c"];
    console.log(alpha.concat(1, [2, 3]));
}
func();

[ 'a', 'b', 'c', 1, 2, 3 ]

Example 3: In this example, the method concat() concatenates both arrays into one array which it returns as the answer.

// JavaScript code for concat() method
function func() {
    let num1 = [[23]];
    let num2 = [89, [67]];
    console.log(num1.concat(num2));
}
func();

[ [ 23 ], 89, [ 67 ] ]

We have a complete list of Javascript Array methods, to check those please go through this Javascript Array Complete reference article.

Supported Browsers:

The browsers supported by the JavaScript Array concat() method are listed below:

• Chrome 51
• Edge 15
• Firefox 54
• Safari 10
• Opera 38

JavaScript Array concat() Method – FAQs

What does the Array.prototype.concat() method do in JavaScript?

The Array.prototype.concat() method is used to merge two or more arrays. It returns a new array containing the elements of the original arrays, in order.

Can concat() be used to add individual elements to an array?

Yes, you can use concat() to add individual elements as well as arrays to an existing array. For example: array1.concat(element1, element2).

How does concat() handle non-array arguments?

If non-array arguments are passed to concat(), they are added as individual elements to the new array.

Can concat() handle nested arrays?

Yes, concat() can handle nested arrays, but it does not flatten them. Nested arrays remain nested in the resulting array.

What are common use cases for the concat() method?

• Merging Arrays: Combining multiple arrays into a single array.
• Adding Elements: Adding individual elements to an array without modifying the original array.
• Creating Copies: Creating shallow copies of arrays by concatenating an empty array.

We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.

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