AsyncIterator : AsyncIterable

<p>

An AsyncIterator is an Object that returns a sequence of Promises.

</p>

<p>

Since AsyncIterators are AsyncIterables, you can use **for await (const value of iterable) {}**

to easily loop over the values in an AsyncIterator.

</p>

<p>

Calling an async generator function (**async function* () {}**) returns

an AsyncIterator.

</p>

<p>

See %%/AsyncIterable|AsyncIterable%% for more details.

</p>

<example>

const sleep = t => new Promise(r => setTimeout(r, t));

const stream = async function*() {

for (let i = 0; i < 3; i++) {

await sleep(300 * i);

yield i;

}

};

const iterator = stream();

console.dir(await iterator.next());

console.dir(await iterator.next());

console.dir(await iterator.next());

console.dir(await iterator.next());

// for-await-of loops make it easy to loop over async iterables

for await (const i of stream()) {

console.log(i);

}

</example>

Spec:

http://www.ecma-international.org/ecma-262/10.0/#sec-asynciterator-interface

----

instance.next([yieldValue : Object]) : Promise

Promise return type:

{ value : Object, done : Boolean }

----

instance.return([yieldValue : Object]) : Promise

----

instance.throw([rejectReason : Object]) : Promise

----

instance[Symbol.asyncIterator] : Function<AsyncIterator>

Returns a method that returns **this**.

<example>

const sleep = t => new Promise(r => setTimeout(r, t));

const stream = async function*() {

for (let i = 0; i < 3; i++) {

await sleep(300 * i);

yield i;

}

};

const iterator = stream();

var iteratorIterator = iterator[Symbol.asyncIterator]();

console.log(iterator === iteratorIterator);

console.log();

for await (const x of stream()) {

console.log(x);

}

console.log();

// Since AsyncIterators are also AsyncIterables, you can use for-await-of loops with them.

for await (const x of iterator) {

console.log(x);

}

</example>