Flatten an Array to a Given Depth in JavaScript

Last Updated : 24 Aug, 2026

Flattening an array in JavaScript means reducing nested arrays to a specified level of depth. This is useful when working with multi-dimensional or nested data structures.

  • The flat() method creates a new array by flattening nested arrays.
  • The depth determines how many levels of nested arrays are flattened.
  • By default, flat() flattens the array up to one level.
  • Passing Infinity as the depth completely flattens an array, regardless of its nesting level.
  • The original array is not modified.

The following approach can be used to flatten a given array up to a specified depth in JavaScript.

Approach: Using the flat() Method

The flat() method recursively concatenates nested arrays up to the specified depth and returns a new flattened array.

Syntax:

array.flat(depth);
  • array: The array that needs to be flattened.
  • depth: The number of levels to flatten. It is optional and defaults to 1.

Example 1: Demonstrates flattening an array to different depths.

JavaScript 
const arr = [1, [2, [3, [4, 5], 6], 7, 8], 9, 10];

console.log("Original Array:", arr);

const flatArrOne = arr.flat(1);

console.log(
    "Array flattened to depth 1:",
    flatArrOne
);

const flatArrTwo = arr.flat(2);

console.log(
    "Array flattened to depth 2:",
    flatArrTwo
);

const flatArrThree = arr.flat(3);

console.log(
    "Array flattened to depth 3:",
    flatArrThree
);

const flatArrComplete = arr.flat(Infinity);

console.log(
    "Array flattened completely:",
    flatArrComplete
);

Output
Original Array: [ 1, [ 2, [ 3, [Array], 6 ], 7, 8 ], 9, 10 ]
Array flattened to depth 1: [ 1, 2, [ 3, [ 4, 5 ], 6 ], 7, 8, 9, 10 ]
Array flattened to depth 2: [ 1, 2, 3, [ 4, 5 ], 6, 7, 8, 9, 10 ]
Arr...

Example 2: Using a Variable for the Depth

The depth can also be stored in a variable when the required level of flattening is determined dynamically.

JavaScript 
const arr = [1, [2, [3, [4, 5]]]];

const depth = 2;

const flattenedArray = arr.flat(depth);

console.log(flattenedArray);

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

Note: The flat() method returns a new array and does not modify the original array. If the complete nested structure needs to be flattened, use flat(Infinity).

Comment

Explore