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This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The flatMap() method first maps each element using a mapping function, then flattens the result into a new array. It is identical to a map followed by a flat of depth 1, but flatMap is quite often useful and merging both into one method is slightly more efficient.

Syntax

var new_array = arr.flatMap(function callback(currentValue[, index[, array]]) {
    // return element for new_array
}[, thisArg])

Parameters

callback
Function that produces an element of the new Array, taking three arguments:
 
currentValue
The current element being processed in the array.
indexOptional
The index of the current element being processed in the array.
arrayOptional
The array map was called upon.
thisArgOptional
Value to use as this when executing callback.

Return value

A new array with each element being the result of the callback function and flattened to a depth of 1.

Description

See Array.prototype.map() for a detailed description of the callback function. The flatMap method is identical to a map followed by a call to flat of depth 1.

Examples

map and flatMap

var arr1 = [1, 2, 3, 4];

arr1.map(x => [x * 2]); 
// [[2], [4], [6], [8]]

arr1.flatMap(x => [x * 2]);
// [2, 4, 6, 8]

// only one level is flattened
arr1.flatMap(x => [[x * 2]]);
// [[2], [4], [6], [8]]
//=> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Alternative

reduce and concat

var arr1 = [1, 2, 3, 4];

arr1.flatMap(x => [x * 2]);
// is equivalent to
arr1.reduce((acc, x) => acc.concat([x * 2]), []);
// [2, 4, 6, 8]
//=> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Specifications

Specification Status Comment
Array.prototype.flatMap proposal Candidate (3)  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support69 No No1 No56 No
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support6969 No No156 No No

1. Available in Firefox Nightly only. See bug 1435813 for status on enabling this by default.

See also

Document Tags and Contributors

Những người đóng góp cho trang này: LJHarb, wmsbill, Baptistou, fscholz
Cập nhật lần cuối bởi: LJHarb,