Iterator.from()
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
The Iterator.from()
static method creates a new Iterator
object from an iterator or iterable object.
Syntax
from(object)
Parameters
Return value
If object
is an iterable, its [Symbol.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.
Description
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:
Examples
Converting an iterable to a proper iterator
Because obj
is already an iterable that returns a proper iterator when its [Symbol.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 [Symbol.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 }
Converting an iterator to a proper iterator
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 }
Specifications
Specification |
---|
Iterator Helpers # sec-iterator.from |
Browser compatibility
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