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AsyncGenerator - JavaScript | MDN

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AsyncGenerator

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since 2020 1.

AsyncGenerator async generator function , .

Promise .

AsyncGenerator AsyncIterator .

In this article

async function* foo() {
  yield await Promise.resolve("a");
  yield await Promise.resolve("b");
  yield await Promise.resolve("c");
}

let str = "";

async function generate() {
  for await (const val of foo()) {
    str = str + val;
  }
  console.log(str);
}

generate();
// Expected output: "abc"

AsyncGenerator JavaScript . AsyncGenerator .

js
async function* createAsyncGenerator() {
  yield await Promise.resolve(1);
  yield await Promise.resolve(2);
  yield await Promise.resolve(3);
}
const asyncGen = createAsyncGenerator();
asyncGen.next().then((res) => console.log(res.value)); // 1
asyncGen.next().then((res) => console.log(res.value)); // 2
asyncGen.next().then((res) => console.log(res.value)); // 3

, . AsyncGenerator.prototype , AsyncGeneratorFunction JavaScript AsyncGeneratorFunction.prototype.prototype . AsyncGenerator AsyncGeneratorFunction.prototype.prototype .

AsyncGenerator.prototype AsyncGenerator .

AsyncGenerator.prototype.constructor

. AsyncGenerator AsyncGeneratorFunction.prototype.

: AsyncGenerator .

AsyncGenerator.prototype[@@toStringTag]

@@toStringTag "AsyncGenerator". Object.prototype.toString() .

AsyncIterator .

AsyncGenerator.prototype.next()

Promise , yield .

AsyncGenerator.prototype.return()

return try...finally .

AsyncGenerator.prototype.throw()

throw .

. 1~6 . for await...of .

js
//  .         .
function delayedValue(time, value) {
  return new Promise((resolve /*, reject*/) => {
    setTimeout(() => resolve(value), time);
  });
}

async function* generate() {
  yield delayedValue(2000, 1);
  yield delayedValue(100, 2);
  yield delayedValue(500, 3);
  yield delayedValue(250, 4);
  yield delayedValue(125, 5);
  yield delayedValue(50, 6);
  console.log("All done!");
}

async function main() {
  for await (const value of generate()) {
    console.log("value", value);
  }
}

main().catch((e) => console.error(e));

Specification
ECMAScript 2027 LanguageSpecification
# sec-asyncgenerator-objects


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