The Symbol.asyncIterator static data property represents the well-known symbol @@asyncIterator. The async iterable protocol looks up this symbol for the method that returns the async iterator for an object. In order for an object to be async iterable, it must have an @@asyncIterator key.

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The well-known symbol @@asyncIterator.

Property attributes of Symbol.asyncIterator
Writable no
Enumerable no
Configurable no


User-defined async iterables

You can define your own async iterable by setting the [Symbol.asyncIterator] property on an object.

const myAsyncIterable = {
  async *[Symbol.asyncIterator]() {
    yield "hello";
    yield "async";
    yield "iteration!";

(async () => {
  for await (const x of myAsyncIterable) {
// Logs:
// "hello"
// "async"
// "iteration!"

When creating an API, remember that async iterables are designed to represent something iterable — like a stream of data or a list —, not to completely replace callbacks and events in most situations.

Built-in async iterables

ReadableStream is the only built-in JavaScript object that has the Symbol.asyncIterator method set by default at the time of writing.


ECMAScript Language Specification
# sec-symbol.asynciterator

Browser compatibility

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See also