TypedArray.prototype.map()

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

// Arrow function
map((currentValue) => { ... } )
map((currentValue, index) => { ... } )
map((currentValue, index, array) => { ... } )

// Callback function
map(callbackFn)
map(callbackFn, thisArg)

// Inline callback function
map(function callbackFn(currentValue) { ... })
map(function callbackFn(currentValue, index) { ... })
map(function callbackFn(currentValue, index, array){ ... })
map(function callbackFn(currentValue, index, array) { ... }, thisArg)

Parameters

callbackFn

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 executing callbackFn.

Return value

A new typed array.

Description

The map() method calls a provided callback function (callbackFn) once for each element in a typed array, in order, and constructs a new typed array from the results.

callbackFn 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.

callbackFn 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 callbackFn 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 callbackFn 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 callbackFn, if invoked, may do so).

The range of elements processed by map() is set before the first invocation of callbackFn. Elements which are appended to the array after the call to map() begins will not be visited by callbackFn. If existing elements of the typed array are changed, or deleted, their value as passed to callbackFn 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 Language Specification (ECMAScript)
# sec-%typedarray%.prototype.map

Browser compatibility

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See also