How to concatenate two arrays in JavaScript

In this tutorial, we are going to learn about how to concatenate the two arrays in JavaScript.

Concatenation means the joining of two or more arrays into a single array.

Consider, we have the following two arrays:

const a = [1, 2, 3];
const b = [4, 5, 6];

Now, we need to join above two arrays like this:

[1, 2, 3, 4, 5, 6]

Using spread operator (…)

To concatenate the two arrays into a single array, we can use the spread(…) operator in JavaScript.

The spread operator unpacks the iterables (such as arrays, objects etc) into a individual elements.

Here is an example:

const a = [1, 2, 3];
const b = [4, 5, 6];

const result = [...a, ...b];
console.log(result);

Output:

[1, 2, 3, 4, 5, 6]

Using concat() Method

Similarly, we can also use the built-in concat() method in JavaScript to concatenate array2 with array1.

The concat() method doesn’t modify the original array, but instead of it returns the new array.

Here is an example:

const a = [1, 2, 3];
const b = [4, 5, 6];

const result = a.concat(b);
console.log(result);

Output:

[1, 2, 3, 4, 5, 6]

We can also concatenate three arrays in JavaScript like this:

const a = [1, 2, 3];
const b = [4, 5, 6];
const c = [7, 8, 9];


const result = a.concat(b, c);
console.log(result);

Output:

[1, 2, 3, 4, 5, 6, 7, 8, 9]