All 10 Async Iterators & Streams questions
More in Async Iterators & Streams
What is an async iterator? How do you loop over an async iterable? What is the ReadableStream API used for? What does return() do on an async iterator? How do you convert a Node.js Readable stream into an async iterable? How do you run multiple async iterators concurrently and merge their results? What's the difference between piping streams with pipeThrough() and pipeTo()? Why might Promise.all() be the wrong tool when consuming many async iterators? How do you add a timeout to an async iterator's next() call?
Advertisement
JavaScript › Async Iterators & Streams

How do you write an async generator function?

Intermediate

Answer

Combine function* with async: async function*. Each yield can await a value first, and calling the generator returns an async iterable you can consume with for-await-of.
async function* fetchPages(url) {
  let next = url;
  while (next) {
    const res = await fetch(next);
    const data = await res.json();
    yield data.items;
    next = data.nextPage;
  }
}
Real-world example Lazily fetching paginated API results page-by-page, only when the consumer asks for more.

Common follow-ups: How would you stop consuming an async generator early?

Iterators & Generators
All 10 Async Iterators & Streams questions