How to Merge/Flatten an array of arrays in JavaScript ?

In this article, we will see how to merge/flat an array of arrays in JavaScript. To do this, first, we create an array of arrays and apply some functions to flat the merged array.

We can Merge/Flatten an array of arrays in Javascript in the following ways:

• Using Array Flat() Method
• Using Spread Operator
• Using Underscore.js _.flatten() Function

Method 1: Using Array Flat() Method

We will create an array of arrays, and then use the flat() method to concatenate the sub-array elements.

Example:

Javascript

let arr = [[1], [2, 3], [4], ["GFG"]];

console.log(arr.flat());

Output

[ 1, 2, 3, 4, 'GFG' ]

Method 2: Using Spread Operator

We can also merge or flatten an array of arrays using the concat() method and the Spread Operator.

Example:

Javascript

const arr = [[1], [2, 3], [4], ["GFG"]];
const flattened = [].concat(...arr);
console.log(flattened);

Output

[ 1, 2, 3, 4, 'GFG' ]

Method 3: Using Underscore.js _.flatten() Function

The _.flatten() function is an inbuilt function in the Underscore.js library of JavaScript which is used to flatten an array that is nested to some level.

For installing Underscore.js, use the below command:

npm install underscore

Javascript

const _ = require('underscore');
console.log(_.flatten([1, [2], [3, [4, [5, [6, [7]]]]]]));

Output:

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