The Symbol.asyncIterator well-known symbol specifies the default AsyncIterator for an object. If this property is set on an object, it is an async iterable and can be used in a for await...of loop.


The Symbol.asyncIterator symbol is a builtin symbol that is used to access an object's @@asyncIterator method. In order for an object to be async iterable, it must have a Symbol.asyncIterator key.

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) {
        // expected output:
        //    "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 are currently no built-in JavaScript objects that have the [Symbol.asyncIterator] key set by default. However, WHATWG Streams are set to be the first built-in object to be async iterable, with [Symbol.asyncIterator] recently landing in the spec.


ECMAScript (ECMA-262)
The definition of 'Symbol.asyncIterator' in that specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
asyncIteratorChrome Full support 63Edge Full support 79Firefox Full support 57IE No support NoOpera Full support 50Safari Full support 11.1WebView Android Full support 63Chrome Android Full support 63Firefox Android No support NoOpera Android Full support 46Safari iOS No support NoSamsung Internet Android Full support 8.0nodejs Full support 10.0.0


Full support  
Full support
No support  
No support

See also