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Mohd Shahid

Posted on

# Hey everyone ðŸ‘‹

Today's article is about two interesting (also important) array methods:

1. `.flat()`
2. `.flatMap()`

## Let's get started ðŸš€

### 1. `.flat()`:

`.flat()` method recusively flattens the elements which are array into the original array and returns a new array.

#### Examples ðŸ‘‡

``````const array = [1,2,[3,4]];
const newArray = array.flat();
console.log(newArray);
// [1,2,3,4]
``````

ðŸ‘‰ `.flat()` receives an optional argument `depth` (1 by default).

``````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]
``````

ðŸ‘‰ The `.flat()` method removes empty slots in arrays:

``````const arr5 = [1, 2, , 4, 5];
arr5.flat();
// [1, 2, 4, 5]
``````

### 2. `.flatMap()`:

`.flatMap()` is identical to a `.map()` followed by a `.flat()` of depth 1.

#### Examples ðŸ‘‡

``````let arr1 = [1, 2, 3, 4];

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

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

ðŸ‘‰ `.flatMap()` only flattens the array up to depth 1.

``````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"]
``````

ðŸ‘‰ 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 ðŸ‘‡

``````// 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. ðŸ˜Š

Take a look on my article on array methods.