All 15 Async Patterns questions
More in Async Patterns
What is the difference between running async operations sequentially with multiple awaits versus concurrently with Promise.all()? How do you implement a retry-with-exponential-backoff pattern for a flaky async operation in Node.js? What is util.promisify(), and when would you still need it in modern Node.js? What is the difference between micro tasks and macro tasks in Node.js's event loop, and how does this affect Promise callback ordering? What is the difference between an unhandled promise rejection and an uncaught exception in Node.js, and how does Node handle each by default? What is a common pitfall when using async/await inside Array.prototype.forEach(), and how do you fix it? How would you implement a concurrency-limited task queue in Node.js to process many async tasks without overwhelming a downstream resource? What is 'fire-and-forget' async code, and why is it generally discouraged in production Node.js applications?
Advertisement
Node.js › Async Patterns

What is an async generator, and how does 'for await...of' let you consume asynchronously produced data?

Advanced

Answer

An async generator (declared with 'async function*') can yield values over time, each potentially resolved from an awaited asynchronous operation, producing an async iterator that a consumer walks through using 'for await...of' -- this is especially useful for processing paginated API results, streaming database cursors, or any data source that arrives incrementally rather than all at once, without needing to load the entire dataset into memory first.
async function* fetchAllPages(url) {
  let nextUrl = url;
  while (nextUrl) {
    const response = await fetch(nextUrl);
    const page = await response.json();
    yield page.items;
    nextUrl = page.nextPageUrl;
  }
}

for await (const items of fetchAllPages('/api/users')) {
  console.log(`Got a page of ${items.length} users`);
}
Real-world example A data-export job consuming a paginated third-party API uses an async generator to yield each page of results as it arrives, processing and writing each batch to disk immediately rather than accumulating potentially hundreds of thousands of records in memory before starting to write anything.

Common follow-ups: How do async generators relate to Node.js readable streams, given both represent asynchronous sequences of data?;What happens if the consuming 'for await...of' loop is exited early with a break -- does the generator clean up properly?

Iterators & Generators;Streams & Buffers
All 15 Async Patterns questions