CODEWITHSUNDEEP
javascriptecmascript-6
user2724541
user2724541

Reputation:

Do generators in Javascript generate an iterator or an iterable object?

I have been reading about iterators and generators a lot lately and from what I have read/seen around, it seems like generators are a syntactic sugar for generating iterators. However, in some code examples, I have also seen the returned value of these generators being used as an iterable. For example:-

function* sampleGenerator() {
 yield 1
 yield 2
 yield 3
}

const it = sampleGenerator()
for (const n of it) {
 console.log(n)
}

I assume that in the for...of loop, the object after the of is an iterable (e.g. arrays, strings etc.). Thus, I am a bit confused about whether the return type is an iterator or an iterable.

Upvotes: 2

Views: 42

Answers (1)

Pingolin
Pingolin

Reputation: 3417

As you can read in the documentation:

A generator object is both iterator and iterable:

let aGeneratorObject = function* () {
  yield 1;
  yield 2;
  yield 3;
}();

console.log(typeof aGeneratorObject.next);
// "function", because it has a next method, so it's an iterator

console.log(typeof aGeneratorObject[Symbol.iterator]);
// "function", because it has an @@iterator method, so it's an iterable

console.log(aGeneratorObject[Symbol.iterator]() === aGeneratorObject);
// true, because its @@iterator method returns itself (an iterator), so it's an well-formed iterable

console.log([...aGeneratorObject]);
// [1, 2, 3]

Upvotes: 3

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