JavaScript Tutorials

JavaScript Array flat()
Syntax & Examples

Array.flat() method

The flat() method of the Array class in JavaScript returns a new array with all sub-array elements concatenated into it recursively up to the specified depth.

Syntax of Array.flat()

There are 2 variations for the syntax of Array.flat() method. They are:

1.
flat()

This method returns a new array with all sub-array elements concatenated into it recursively up to a depth of 1.

Returns value of type Array.

2.
flat(depth)

Parameters

ParameterOptional/RequiredDescription
depthoptionalThe depth level specifying how deep a nested array structure should be flattened. Defaults to 1.

This method returns a new array with all sub-array elements concatenated into it recursively up to the specified depth.

Returns value of type Array.


✐ Examples

1 Using flat() method to flatten an array with default depth

In JavaScript, we can use the flat() method to flatten an array with the default depth of 1.

For example,

  1. We define an array variable arr with nested elements [1, [2, [3, [4]], 5]].
  2. We use the flat() method on arr to flatten it with the default depth of 1.
  3. The result is stored in the variable flattenedArr.
  4. We log flattenedArr to the console using console.log() method to see the flattened array.

JavaScript Program

const arr = [1, [2, [3, [4]], 5]];
const flattenedArr = arr.flat();
console.log(flattenedArr);

Output

[1, 2, [3, [4]], 5]

2 Using flat() method to flatten an array with specified depth

We can use the flat() method to flatten an array to a specified depth.

For example,

  1. We define an array variable arr with nested elements [1, [2, [3, [4]], 5]].
  2. We use the flat() method on arr with the depth parameter set to 2.
  3. The result is stored in the variable flattenedArr.
  4. We log flattenedArr to the console using console.log() method to see the flattened array.

JavaScript Program

const arr = [1, [2, [3, [4]], 5]];
const flattenedArr = arr.flat(2);
console.log(flattenedArr);

Output

[1, 2, 3, [4], 5]

Summary

In this JavaScript tutorial, we learned about flat() method of Array: the syntax and few working examples with output and detailed explanation for each example.