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.

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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 executing mapFn.

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

Browser compatibility

See also

• TypedArray.prototype.filter()
• Array.prototype.map()