events.once(emitter, name)


创建一个 Promise,当 EventEmitter 触发给定的事件时则会被解决,当 EventEmitter 触发 'error' 时则会被拒绝。 解决 Promise 时将会带上触发到给定事件的所有参数的数组。

此方法是有意通用的,并且可与 Web 平台的 EventTarget 接口一起使用,该接口没有特殊的 'error' 事件语义且不监听 'error' 事件。

const { once, EventEmitter } = require('events');

async function run() {
  const ee = new EventEmitter();

  process.nextTick(() => {
    ee.emit('myevent', 42);
  });

  const [value] = await once(ee, 'myevent');
  console.log(value);

  const err = new Error('错误信息');
  process.nextTick(() => {
    ee.emit('error', err);
  });

  try {
    await once(ee, 'myevent');
  } catch (err) {
    console.log('出错', err);
  }
}

run();

Creates a Promise that is fulfilled when the EventEmitter emits the given event or that is rejected when the EventEmitter emits 'error'. The Promise will resolve with an array of all the arguments emitted to the given event.

This method is intentionally generic and works with the web platform EventTarget interface, which has no special 'error' event semantics and does not listen to the 'error' event.

const { once, EventEmitter } = require('events');

async function run() {
  const ee = new EventEmitter();

  process.nextTick(() => {
    ee.emit('myevent', 42);
  });

  const [value] = await once(ee, 'myevent');
  console.log(value);

  const err = new Error('kaboom');
  process.nextTick(() => {
    ee.emit('error', err);
  });

  try {
    await once(ee, 'myevent');
  } catch (err) {
    console.log('error happened', err);
  }
}

run();