AsyncGenerator.prototype.next()

main Documentación oficial Licencia CC-BY-SA-2.5Descargado el 2026-08-02

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Syntax#
Parameters#
Return value#
Examples#
Using next()#
Sending values to the generator#
Specifications#
Browser compatibility#
See also#

The next() method of {{jsxref("AsyncGenerator")}} instances returns the next value in the sequence.

Syntax#

next()
next(value)

Parameters#

value {{optional_inline}}
: An optional value used to modify the internal state of the generator. A value passed to the next() method will be received by yield

Return value#

A {{jsxref("Promise")}} which when resolved returns an {{jsxref("Object")}} with two properties:

done
: A boolean value:
- true if the generator is past the end of its control flow. In this case value specifies the return value of the generator (which may be undefined).
- false if the generator is able to produce more values.
value
: Any JavaScript value yielded or returned by the generator.

Examples#

Using next()#

The following example shows a generator and the object that the next method returns:

// An async task. Pretend it's doing something more useful
// in practice.
function delayedValue(time, value) {
  return new Promise((resolve, reject) => {
    setTimeout(() => resolve(value), time);
  });
}

async function* createAsyncGenerator() {
  yield delayedValue(500, 1);
  yield delayedValue(500, 2);
  yield delayedValue(500, 3);
}

const asyncGen = createAsyncGenerator();
asyncGen.next().then((res) => console.log(res)); // { value: 1, done: false }
asyncGen.next().then((res) => console.log(res)); // { value: 2, done: false }
asyncGen.next().then((res) => console.log(res)); // { value: 3, done: false }
asyncGen.next().then((res) => console.log(res)); // { value: undefined, done: true }

Sending values to the generator#

In this example, next is called with a value.

[!NOTE] The first call does not log anything, because the generator was not yielding anything initially.

// An async task. Pretend it's doing something more useful
// in practice.
function sleep(time) {
  return new Promise((resolve, reject) => {
    setTimeout(resolve, time);
  });
}

async function* createAsyncGenerator() {
  while (true) {
    await sleep(500);
    const value = yield;
    console.log(value);
  }
}

async function main() {
  const asyncGen = createAsyncGenerator();
  // No log at this step: the first value sent through `next` is lost
  console.log(await asyncGen.next(1)); // { value: undefined, done: false }
  // Logs 2: the value sent through `next`
  console.log(await asyncGen.next(2)); // { value: undefined, done: false }
}

main();