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Kritika Pattalam Bharathkumar

Posted on • Originally published at blog.kritikapattalam.com

# 2 Uses of concat method when working with arrays in JavaScript

Let's see two ways in which concat() method can be used while working with arrays in JavaScript.

### 1) Merging two or more arrays

Let's now see how we can use the concat method to merge two given arrays, array 1 and array 2

``````const array1 = [1,2,3,4];
const array2 = [5,6,7];
// merge array 1 into array 2 and store it in a new variable
const newMergedArray = [].concat(array1, array2);
console.log(newMergedArray); // [1, 2, 3, 4, 5, 6, 7]
console.log(array1); // [1, 2, 3, 4]
console.log(array2); // [5,6,7]
``````

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

In the above line [] creates a new array and the concat methods combine both array1, array2. This can also accept more than 2 arrays for concatenation by just adding them one next to the other

const newMergedArray = [].concat(array1, array2, array 3, arrayN);

Another alternative for merging two arrays is below

const newMergedArray = array1.concat(array2, array 3, arrayN);

### 2) Flatten single level nested arrays

Let's assume there is a nested array as below, and we would want to flatten it in such a way that the output is [1,2,3,4,5,6,7,8], this can be achieved by using concat() method with the help of spread operator.

``````const array1 = [1,2,[3,4],[5,6], 7, 8];
const flattened = [].concat(...array1);
console.log(flattened); // [1,2,3,4,5,6,7,8]
``````

P.S. The above code flattens just a single-level nested array.

### Check out my other blog posts

To merge: `[...ar1,...ar2]`