JavaScriptArrays

Array.prototype.flat()

Flattens nested arrays down to the given depth.

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Example

JavaScript

const nested = [1, [2, 3], [4, [5, [6]]]]

console.log(nested.flat())
console.log(nested.flat(2))
console.log(nested.flat(Infinity))

Console

[1, 2, 3, 4, [5, [6]]]

[1, 2, 3, 4, 5, [6]]

[1, 2, 3, 4, 5, 6]

The flat() method creates a new array in which nested arrays are unpacked into individual elements. By default it flattens one level of nesting.

The argument sets the depth: flat(2) flattens two levels, and flat(Infinity) flattens all of them, no matter how deep.

Along the way it also removes holes in sparse arrays. The original array doesn’t change.

array.flat()
array.flat(depth)

Parameter	Type	Description
depth	optional	The number of levels to flatten. Defaults to 1.

Widely available

Works in all modern browsers, phones included. You can use it without worry.

If you map first and then flatten, use flatMap() instead of map().flat().
flat(Infinity) is convenient, but on unknown, very deep data it can get expensive.

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