Symbol.asyncIterator

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

The Symbol.asyncIterator static data property represents the well-known symbol 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 [Symbol.asyncIterator] key.

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Value

The well-known symbol Symbol.asyncIterator.

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

Examples

User-defined async iterables

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

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

(async () => {
  for await (const x of myAsyncIterable) {
    console.log(x);
  }
})();
// 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

There is no object in the core JavaScript language that is async iterable. Some web APIs, such as ReadableStream, have the Symbol.asyncIterator method set by default.

Specifications

Specification
ECMAScript Language Specification
# sec-symbol.asynciterator

Browser compatibility

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See also