Merge different arrays in JavaScript

An array is a data structure representing an ordered collection of indexed items.

A common operation performed on multiple arrays is merge — when 2 or more arrays are merged to form a bigger array containing all the items of the merged arrays.

We can use the ES6 spread operator to merge different arrays into one:

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

The spread operator is handy if we use the `push` method as well:

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

a.push(...b);
a; // [1, 2, 3, 4, 5, 6]