TypedArray.from()
The TypedArray.from()
method creates a new
typed array
from an array-like or iterable object. This method is nearly the same as
Array.from()
.
Syntax
// Arrow function
TypedArray.from(arrayLike, (element) => { /* ... */ } )
TypedArray.from(arrayLike, (element, index) => { /* ... */ } )
// Mapping function
TypedArray.from(arrayLike, mapFn)
TypedArray.from(arrayLike, mapFn, thisArg)
// Inline mapping function
TypedArray.from(arrayLike, function mapFn(element) { /* ... */ })
TypedArray.from(arrayLike, function mapFn(element, index) { /* ... */ })
TypedArray.from(arrayLike, function mapFn(element) { /* ... */ }, thisArg)
TypedArray.from(arrayLike, function mapFn(element, index) { /* ... */ }, thisArg)
Where TypedArray
is one of:
Parameters
arrayLike
-
An array-like or iterable object to convert to a typed array.
mapFn
Optional-
Map function to call on every element of the typed array.
thisArg
Optional-
Value to use as
this
when executingmapFn
.
Return value
A new TypedArray
instance.
Description
TypedArray.from()
lets you create typed arrays from:
-
array-like objects (objects with a
length
property and indexed elements); or -
iterable objects (objects
where you can get its elements, such as
Map
andSet
).
TypedArray.from()
has the optional parameter
mapFn
, which allows you to execute a
map()
function on each element of the typed array
(or subclass object) that is being created. This means that the following are
equivalent:
TypedArray.from(obj, mapFn, thisArg)
TypedArray.from(Array.prototype.map.call(obj, mapFn, thisArg))
.
The length
property of the from()
method is 1
.
Differences from Array.from()
Some subtle distinctions between Array.from()
and
TypedArray.from()
:
-
If the
thisArg
value passed toTypedArray.from()
is not a constructor,TypedArray.from()
will throw aTypeError
, whereArray.from()
defaults to creating a newArray
. -
TypedArray.from()
uses[[Put]]
whereArray.from()
uses[[DefineProperty]]
. Hence, when working withProxy
objects, it callshandler.set
to create new elements rather thanhandler.defineProperty()
. -
When the
source
parameter is an iterator, theTypedArray.from()
first collects all the values from the iterator, then creates an instance ofthisArg
using the count, then sets the values on the instance.Array.from()
sets each value as it receives them from the iterator, then sets itslength
at the end. -
When
Array.from()
gets an array-like which isn't an iterator, it respects holes.TypedArray.from()
will ensure the result is dense.
Examples
From an iterable object (Set)
const s = new Set([1, 2, 3]);
Uint8Array.from(s);
// Uint8Array [ 1, 2, 3 ]
From a string
Int16Array.from('123');
// Int16Array [ 1, 2, 3 ]
Use with arrow function and map
Using an arrow function as the map function to manipulate the elements
Float32Array.from([1, 2, 3], x => x + x);
// Float32Array [ 2, 4, 6 ]
Generate a sequence of numbers
Uint8Array.from({length: 5}, (v, k) => k);
// Uint8Array [ 0, 1, 2, 3, 4 ]
Specifications
Specification |
---|
ECMAScript Language Specification # sec-%typedarray%.from |
Browser compatibility
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