Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The Iterator.from()
static method creates a new Iterator
object from an iterator or iterable object.
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The Iterator.from()
static method creates a new Iterator
object from an iterator or iterable object.
from(object)
If object
is an iterable, its @@iterator
method is called to obtain the iterator. Otherwise, object
is assumed to be an iterator. If the iterator is already instanceof
Iterator
(which means it has Iterator.prototype
in its prototype chain), it is returned directly. Otherwise, a new Iterator
object is created that wraps the original iterator.
This method exists to convert custom iterators, probably exported by libraries, to proper iterators. All iterator objects returned by Iterator.from()
inherit from a common prototype object, which has the following methods:
Because obj
is already an iterable that returns a proper iterator when its @@iterator
method is called, Iterator.from(obj)
returns the same iterator.
const iterator = (function* () { yield 1; yield 2; yield 3; })(); const obj = { [Symbol.iterator]() { return iterator; }, }; const iterator2 = Iterator.from(obj); console.log(iterator2 === iterator); // true
Because obj2
is an iterable that returns a non-proper iterator when its @@iterator
method is called, Iterator.from(obj2)
returns a new iterator that wraps the original iterator.
const iterator = { current: 0, next() { return { value: this.current++, done: false }; }, }; const obj2 = { [Symbol.iterator]() { return iterator; }, }; const iterator2 = Iterator.from(obj2); console.log(iterator2 === iterator); // false console.log(iterator2.next()); // { value: 0, done: false } console.log(iterator.next()); // { value: 1, done: false }
Because obj
is already a proper iterator, Iterator.from(obj)
returns itself.
const obj = (function* () { yield 1; yield 2; yield 3; })(); const iterator = Iterator.from(obj); console.log(iterator === obj); // true
Because obj2
is a non-proper iterator, Iterator.from(obj2)
returns a new iterator that wraps the original iterator.
const obj2 = { current: 0, next() { return { value: this.current++, done: false }; }, }; const iterator = Iterator.from(obj2); console.log(iterator === obj2); // false console.log(iterator.next()); // { value: 0, done: false } console.log(obj2.next()); // { value: 1, done: false }
Specification |
---|
Iterator Helpers # sec-iterator.from |
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | Deno | Node.js | ||
from |
117 | 117 | No | 103 | No | 117 | No | 78 | No | No | 117 | No | No |
© 2005–2023 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator/from