# 2 Important! Array methods you should know.

# Hey everyone 👋
Today's article is about two interesting (*also important*) array methods:  
1. `.flat()`   
2. `.flatMap()`  

### Let's get started 🚀
#### 1. `.flat()`:
`.flat()` method recusively flattens the elements which are array into the original array and returns a new array.  
 #### Examples 👇
```js
const array = [1,2,[3,4]];
const newArray = array.flat();
console.log(newArray);
// [1,2,3,4]
```
👉 `.flat()` receives an optional argument `depth` (1 by default).

```js
const arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat();
// [1, 2, 3, 4, [5, 6]]

const arr3 = [1, 2, [3, 4, [5, 6]]];
arr3.flat(2);
// [1, 2, 3, 4, 5, 6]
```
👉 The `.flat()` method removes empty slots in arrays:
```js
const arr5 = [1, 2, , 4, 5];
arr5.flat();
// [1, 2, 4, 5]
```
<hr />
#### 2. `.flatMap()`:  
`.flatMap()` is identical to a `.map()` followed by a `.flat()` of depth 1.  

 #### Examples 👇
```js
let arr1 = [1, 2, 3, 4];

arr1.map(x => [x * 2]);
// [[2], [4], [6], [8]]

arr1.flatMap(x => [x * 2]);
// [2, 4, 6, 8]
```
👉 `.flatMap()` only flattens the array up to depth 1.  
```js
let arr1 = ["it's Sunny in", "", "California"];

arr1.map(x => x.split(" "));
// [["it's","Sunny","in"],[""],["California"]]

arr1.flatMap(x => x.split(" "));
// ["it's","Sunny","in", "", "California"]
```

👉 As you know `.map` always works *one-to-one*, but `flatMap` can be used to modify the number of items during `map`.

A nice example I found on MDN 👇
```js
// Let's say we want to remove all the negative numbers
// and split the odd numbers into an even number and a 1
let a = [5, 4, -3, 20, 17, -33, -4, 18]
//       |\  \  x   |  | \   x   x   |
//      [4,1, 4,   20, 16, 1,       18]

a.flatMap( (n) =>
  (n < 0) ?      [] :
  (n % 2 == 0) ? [n] :
                 [n-1, 1]
)

// [4, 1, 4, 20, 16, 1, 18]
```

That's it for this article, I hope you found it useful. 😊  
Take a look on my article on [array methods](https://sidmirza.hashnode.dev/array-methods-in-javascript-when-to-use-which).  
Please leave a like and follow me on [twitter](https://www.twitter.com/sidmirza4).  
#### Thanks for reading. 💚  
#### Happy coding.