The **``flat`` function** in JavaScript is used to flatten a nested array.

For example, if an array exists within an array, the ``flat`` function can be used to concatenate the two arrays into one. One can do this by merging the inner array elements with those of the outer one.
> The ``flat`` function also removes any empty spaces.
# Syntax
```Javascript
flat()
```
**OR** 

```Javascript
flat(depth)
```
# Parameters
The ``flat`` function takes up to 1 argument:

* **``depth``** - a value to limit flattening to a certain depth or nesting level. For instance, a depth of 1 will only flatten a 2D array.

> ``depth`` is an optional parameter. By default, it is assumed to be 1.

# Return value
The ``flat`` function returns the flattened array.

# Example

The program below declares a nested array with a depth of `2`. The ``flat`` function is called without specifying ``depth``; hence, it is assumed to be `1`.

The first call to ``flat`` partially flattens the array; subsequently, ``flat`` is called again with a depth of ``2``. The original array is now fully flattened.

The previous and modified arrays are printed using the ``console.log`` function so that you can observe the differences between them. 

// Declare a nested array with depth 2
const sample_array = [1, 2, [3, 4, [5, 6]]];
// Call flat function with depth 1. Original array partially flattened.
const single_flattened = sample_array.flat()
// Call flat function with depth 2. Original array fully flattened.
const double_flattened = sample_array.flat(2)

console.log(sample_array)
// [1, 2, [3, 4, [5, 6]]]
console.log(single_flattened)
// [1, 2, 3, 4, [5, 6]]
console.log(double_flattened)
//[1, 2, 3, 4, 5, 6]

What is the flat function in JavaScript?

Syntax

Parameters

Return value

Example