What are JS Generators?

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What are JS Generators?

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


You can create generators like this:

function* myGenerator() {}

The * after function is required.


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 (2)

Todd Pressley's photo

I've been curious for some time now about generators. They seem incredibly powerful; yet I've never used them IRL. What are some real-world use cases for generators?

shadowtime2000's photo

I believe they are mainly for readable iterators.