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.
Syntax
typedarray.map(callback[, thisArg])
Parameters
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
- The index of the current element being processed in the typed array.
array
- The typed array
map
was called upon.
thisArg
- Optional. Value to use as
this
when executingcallback
.
Return value
A new typed array.
Description
The map
method calls a provided callback
function once for each element in a typed array, in order, and constructs a new typed array from the results. callback
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.
callback
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 callback
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 callback
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 callback
, if invoked, may do so).
The range of elements processed by map
is set before the first invocation of callback
. Elements which are appended to the array after the call to map
begins will not be visited by callback
. If existing elements of the typed array are changed, or deleted, their value as passed to callback
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.
var numbers = new Uint8Array([1, 4, 9]); var 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.
var numbers = new Uint8Array([1, 4, 9]); var doubles = numbers.map(function(num) { return num * 2; }); // doubles is now Uint8Array [2, 8, 18] // numbers is still Uint8Array [1, 4, 9]
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'TypedArray.prototype.map' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'TypedArray.prototype.map' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | 38 (38) | No support | No support | No support |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | No support | 38.0 (38) | No support | No support | No support |