events once emitter name

• emitter {EventEmitter}
• name {string}
• 返回: {Promise}

创建一个 Promise，当 EventEmitter 触发给定的事件时则会被解决，如果等待时 EventEmitter 触发 'error' 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][WHATWG-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();

The special handling of the 'error' event is only used when events.once() is used to wait for another event. If events.once() is used to wait for the ‘error' event itself, then it is treated as any other kind of event without special handling:

const { EventEmitter, once } = require('events');
const ee = new EventEmitter();
once(ee, 'error')
  .then(([err]) => console.log('ok', err.message))
  .catch((err) => console.log('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom