Symbol.asyncIterator
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.
Description
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 |
Examples
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) {
console.log(x);
// 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.
Specifications
Specification |
---|
ECMAScript Language Specification # sec-symbol.asynciterator |
Browser compatibility
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