# How to deep flatten an array in JavaScript?

JavascriptObject Oriented ProgrammingProgramming

## Flattening an array

Flattening an array is nothing but merging a group of nested arrays present inside a provided array.

## 1) concat.apply()

In the following example there are some nested arrays containing elements 3,4,5 and 6. After flattening them using concat() method we get the output as 1,2,3,4,5,6,9.

### Example

Live Demo

<html>
<body>
<script>
var arrays = [1,2,[3,4,[5,6]],9];
var merged = [].concat.apply([], arrays);
documemt.write(merged);
</script>
</body>
</html>

### Output

1,2,3,4,5,6,9

## 2) array.flat()

In the following example there are some nested elements such as 2,3,4,5,6,9. After Flattening them using array.flat() method we get the output as 1,2,2,3,4,5,6,9.

### Example

Live Demo

<html>
<body>
<script>
const arrays = [1,2,[2,3,[4,5,[6,9]]]];
const merged = arrays.flat(2);
document.write(merged)
</script>
</body>
</html>

### Output

1,2,2,3,4,5,6,9
Published on 10-Jun-2019 15:28:59