# Array Flatten in JavaScript

**What are Nested Arrays?**

A nested array is an array inside another array.

Eg. const arr = \[b, c, \[a, e, i, o, u\], d, \[f, g\]\]

**Why flattening arrays is useful?**

Flattening of arrays in JavaScript involves merging multiple nested arrays into a single array. It helps with easier data processing and simplifies operations.

Flattening = removing all layers of nesting

**Different approaches to flatten arrays**

*   We use array.flat() method primarily to flatten an array. This creates a new array with all the sub elements concatenated to it.
    

Eg. let arr = \[10, \[20, 30\], \[40, \[50, 60\]\], 70\]

let flatArr = arr.flat(Infinity);

console.log(flatArr);

Output: \[10, 20, 30, 40, 50, 60, 70\]

*   Using recursion, which means repeating the same process for nested arrays until everything has been flattened.
    

Eg. function flattenArray(arr){

let result = \[\]

function flatten(elem){

if (Array.isArray(elem)){

for (let i =0; i < elem. length; i++){

flatten(elem\[i\]);

}} else {

result.push(elem)

}}

flatten(arr)

return result

}

if the element turns out to be array then recurse else push.

*   Using reduce
    

Eg. function flatten(arr){

return arr.reduce((acc, curr) => {

return acc.concat(

Array.isArray(curr) ? flatten(curr) : curr

)

}, \[\])

}

![](https://cdn.hashnode.com/uploads/covers/697ce1532c2f80ee0dc0c921/3bbd09c0-21c3-4a08-82de-0e384209e344.png align="center")