TypedArray.from()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.
The TypedArray.from()
static method creates a new
typed array
from an array-like or iterable object. This method is nearly the same as
Array.from()
.
Try it
Syntax
TypedArray.from(arrayLike, mapFn)
TypedArray.from(arrayLike, mapFn, thisArg)
Where TypedArray
is one of:
Parameters
arrayLike
-
An iterable or array-like object to convert to a typed array.
mapFn
Optional-
A function to call on every element of the typed array. If provided, every value to be added to the array is first passed through this function, and
mapFn
's return value is added to the typed array instead. The function is called with the following arguments: thisArg
Optional-
Value to use as
this
when executingmapFn
.
Return value
A new TypedArray
instance.
Description
See Array.from()
for more details.
There are some subtle distinctions between Array.from()
and TypedArray.from()
(note: the this
value mentioned below is the this
value that TypedArray.from()
was called with, not the thisArg
argument used to invoke mapFn
):
- If the
this
value ofTypedArray.from()
is not a constructor,TypedArray.from()
will throw aTypeError
, whileArray.from()
defaults to creating a newArray
. - The object constructed by
this
must be aTypedArray
instance, whileArray.from()
allows itsthis
value to be constructed to any object. - When the
source
parameter is an iterator,TypedArray.from()
first collects all the values from the iterator, then creates an instance ofthis
using the count, and finally sets the values on the instance.Array.from()
sets each value as it receives them from the iterator, then sets itslength
at the end. TypedArray.from()
uses[[Set]]
whileArray.from()
uses[[DefineOwnProperty]]
. Hence, when working withProxy
objects, it callshandler.set()
to create new elements rather thanhandler.defineProperty()
.- 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 ]
Calling from() on non-TypedArray constructors
The this
value of from()
must be a constructor that returns a TypedArray
instance.
function NotArray(len) {
console.log("NotArray called with length", len);
}
Int8Array.from.call({}, []); // TypeError: #<Object> is not a constructor
Int8Array.from.call(NotArray, []);
// NotArray called with length 0
// TypeError: Method %TypedArray%.from called on incompatible receiver #<NotArray>
function NotArray2(len) {
console.log("NotArray2 called with length", len);
return new Uint8Array(len);
}
console.log(Int8Array.from.call(NotArray2, [1, 2, 3]));
// NotArray2 called with length 3
// Uint8Array(3) [ 1, 2, 3 ]
Specifications
Specification |
---|
ECMAScript Language Specification # sec-%typedarray%.from |
Browser compatibility
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