The map()
method creates a new typed array with the results of calling a provided function on every element in this typed array. This method has the same algorithm as Array.prototype.map()
. TypedArray is one of the typed array types here.
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Syntax
typedArray.map(mapFn[, thisArg])
Parameters
mapFn
-
A callback function that produces an element of the new typed array, taking three arguments:
currentValue
- The current element being processed in the typed array.
index
Optional- The index of the current element being processed in the typed array.
array
Optional- The typed array
map()
was called upon.
thisArg
Optional- Value to use as
this
when executingmapFn
.
Return value
A new typed array.
Description
The map()
method calls a provided callback function (mapFn
) once for each element in a typed array, in order, and constructs a new typed array from the results.
mapFn
is invoked only for indexes of the typed array which have assigned values; it is not invoked for indexes that are undefined
, those which have been deleted, or which have never been assigned values.
mapFn
is invoked with three arguments: the value of the element, the index of the element, and the typed array object being traversed.
If a thisArg
parameter is provided to map()
, it will be passed to mapFn
when invoked, for use as its this
value. Otherwise, the value undefined
will be passed for use as its this
value. The this
value ultimately observable by mapFn
is determined according to the usual rules for determining the this
seen by a function.
map()
does not mutate the typed array on which it is called (although mapFn
, if invoked, may do so).
The range of elements processed by map()
is set before the first invocation of mapFn
. Elements which are appended to the array after the call to map()
begins will not be visited by mapFn
. If existing elements of the typed array are changed, or deleted, their value as passed to mapFn
will be the value at the time map()
visits them; elements that are deleted are not visited.
Examples
Mapping a typed array to a typed array of square roots
The following code takes a typed array and creates a new typed array containing the square roots of the numbers in the first typed array.
const numbers = new Uint8Array([1, 4, 9]); const roots = numbers.map(Math.sqrt); // roots is now: Uint8Array [1, 2, 3], // numbers is still Uint8Array [1, 4, 9]
Mapping a typed array of numbers using a function containing an argument
The following code shows how map works when a function requiring one argument is used with it. The argument will automatically be assigned to each element of the typed array as map loops through the original typed array.
const numbers = new Uint8Array([1, 4, 9]); const doubles = numbers.map(function(num) { return num * 2; }); // doubles is now Uint8Array [2, 8, 18] // numbers is still Uint8Array [1, 4, 9]
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'TypedArray.prototype.map' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
map | Chrome Full support 45 | Edge Full support 14 | Firefox Full support 38 | IE No support No | Opera Full support 32 | Safari No support No | WebView Android Full support 45 | Chrome Android Full support 45 | Firefox Android Full support 38 | Opera Android Full support 32 | Safari iOS No support No | Samsung Internet Android Full support 5.0 | nodejs Full support 4.0.0 |
Legend
- Full support
- Full support
- No support
- No support