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JavaScript - add array to array

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Created by:
Niac
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In this article, we would like to show you how to add array to array in JavaScript.

There are two most common ways how to add array to an array:

  1. Using the spread operator.
  2. Using concat() method,

1. Spread operator example 

Below example shows how to use spread operator (...) to create a new array3 object which is a combination of two arrays.

// ONLINE-RUNNER:browser;

const array1 = ['1', '2'];
const array2 = ['3', '4'];
const array3 = [...array1, ...array2]

console.log(array3); // 1,2,3,4

2. concat() method example

We can use the method on an empty array [] and pass two arrays we want to merge as arguments.

Runnable example:

// ONLINE-RUNNER:browser;

const array1 = ['1', '2'];
const array2 = ['3', '4'];
const array3 = [].concat(array1, array2);

console.log(array3); // 1,2,3,4

We can also use concat() method on the existing array and pass just one argument - the array we want to merge our base array with.

Runnable example: 

// ONLINE-RUNNER:browser;

const array1 = ['1', '2'];
const array2 = ['3', '4'];
const array3 = array1.concat(array2);

console.log(array3); // 1,2,3,4

Merging arrays in different order example:

// ONLINE-RUNNER:browser;

const array1 = ['1', '2'];
const array2 = ['3', '4'];

const array3 = [].concat(array2, array1);
const array4 = array2.concat(array1);

console.log(array3); // 3,4,1,2
console.log(array4); // 3,4,1,2

Note:
Using .concat() on existing array doesn't manipulate or change the existing array.

References

JavaScript - Arrays (popular problems)

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