What are JS Generators?

Generators are a feature in Javascript which are basically functions that are kind of like iterators.

Creating

You can create generators like this:

function* myGenerator() {}

The * after function is required.

Yielding

The core mechanic of generators is yielding values.

function* myGenerator() {
    yield 1;
    yield "foo";
    yield "bar";
    yield { thing: true };
}

Taking Values

You have created your generator. Now, we need to use it. When you have a generator, you can call .next() on it, and it will run the generator until it reaches a yield statement. When it reaches it, it will return an object with two parameters, value, and done.

const one = myGenerator.next().value; // 1
const foo = myGenerator.next().value; // "foo"
const bar = myGenerator.next().value; // "bar"
const thingTrue = myGenerator.next().value; // { thing: true }

MDN Docs

You can look more into generators on the MDN docs.

Comments

[Usman Khalil]

What are common use cases for generators?

[shadowtime2000]

I think mainly they are for creating more readable iterators.