JavaScript Array flat Method (Live Playground)

The JavaScript Array flat method is used to flatten an array, which means it converts a multi-dimensional array into a single-dimensional array.

Here's a basic example of how you can use the flat method:

let nestedArray = [1, [2, 3], [4, [5, 6]]];
let flattenedArray = nestedArray.flat();

console.log(flattenedArray);

// Expected output:
// [1, 2, 3, 4, [5, 6]]

In the example above, nestedArray.flat() creates a new array that's one level less nested than the original. The default depth that flat flattens is 1.

Live Playground, Try it Yourself

JavaScript / TypeScript

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let nestedArray = [1, [2, 3], [4, [5, 6]]];

let flattenedArray = nestedArray.flat();

console.log(flattenedArray);

Preview

Console

You can also specify the depth to which you want to flatten the array:

let deeplyNestedArray = [1, [2, [3, [4, [5]]]]];
let deeplyFlattenedArray = deeplyNestedArray.flat(4);

console.log(deeplyFlattenedArray);

// Expected output:
// [1, 2, 3, 4, 5]

In this second example, deeplyNestedArray.flat(4) flattens the array to 4 levels deep, resulting in a completely flattened array.

Live Playground, Try it Yourself

JavaScript / TypeScript

9

1

2

3

4

let deeplyNestedArray = [1, [2, [3, [4, [5]]]]];

let deeplyFlattenedArray = deeplyNestedArray.flat(4);

console.log(deeplyFlattenedArray);

Preview

Console

Using the flat method can simplify your code when you're working with nested arrays in JavaScript.