Symbol.asyncIterator
The Symbol.asyncIterator
static data property represents the well-known symbol specifying the method that returns the async iterator 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.
Try it
Value
The well-known symbol @@asyncIterator
.
Property attributes of Symbol.asyncIterator |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
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.
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);
}
})();
// 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.
Specifications
Specification |
---|
ECMAScript Language Specification # sec-symbol.asynciterator |
Browser compatibility
BCD tables only load in the browser