The next() method returns the next value in the sequence.



value Optional

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 Promise which when resolved returns an Object with two properties:


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.

Any JavaScript value yielded or returned by the generator.


Using next()

The following example shows a simple 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(); => console.log(res));    // { value: 1, done: false } => console.log(res));    // { value: 2, done: false } => console.log(res));    // { value: 3, done: false } => 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;

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



ECMAScript Language Specification
# sec-asyncgenerator-prototype-next

Browser compatibility

BCD tables only load in the browser

See also