events.on(emitter, eventName[, options])

• emitter <EventEmitter>
• eventName <string> | <symbol> 正在监听的事件的名称
• options <Object>
  • signal <AbortSignal> 可用于取消等待事件。
• 返回: <AsyncIterator> 迭代由 emitter 触发的 eventName 事件

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

// 稍后触发
process.nextTick(() => {
  ee.emit('foo', 'bar');
  ee.emit('foo', 42);
});

for await (const event of on(ee, 'foo')) {
  // 此内部块的执行是同步的，
  // 它一次处理一个事件（即使有等待）。
  // 如果需要并发执行，则不要使用。
  console.log(event); // 打印 ['bar'] [42]
}
// 此处无法到达const { on, EventEmitter } = require('node:events');

(async () => {
  const ee = new EventEmitter();

  // 稍后触发
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo')) {
    // 此内部块的执行是同步的，
    // 且每次处理一个事件（即使有等待）。
    // 如果需要并发执行，则不要使用。
    console.log(event); // 打印 ['bar'] [42]
  }
  // 此处无法到达
})();

返回迭代 eventName 事件的 AsyncIterator。 如果 EventEmitter 触发 'error'，则将抛出错误。 它在退出循环时删除所有监听器。 每次迭代返回的 value 是由触发的事件参数组成的数组。

<AbortSignal> 可用于取消对事件的等待：

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ac = new AbortController();

(async () => {
  const ee = new EventEmitter();

  // 稍后触发
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo', { signal: ac.signal })) {
    // 此内部块的执行是同步的，
    // 且每次处理一个事件（即使有等待）。
    // 如果需要并发执行，则不要使用。
    console.log(event); // 打印 ['bar'] [42]
  }
  // 此处无法到达
})();

process.nextTick(() => ac.abort());const { on, EventEmitter } = require('node:events');

const ac = new AbortController();

(async () => {
  const ee = new EventEmitter();

  // 稍后触发
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo', { signal: ac.signal })) {
    // 此内部块的执行是同步的，
    // 且每次处理一个事件（即使有等待）。
    // 如果需要并发执行，则不要使用。
    console.log(event); // 打印 ['bar'] [42]
  }
  // 此处无法到达
})();

process.nextTick(() => ac.abort());

• emitter <EventEmitter>
• eventName <string> | <symbol> The name of the event being listened for
• options <Object>
  • signal <AbortSignal> Can be used to cancel awaiting events.
• Returns: <AsyncIterator> that iterates eventName events emitted by the emitter

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
  ee.emit('foo', 'bar');
  ee.emit('foo', 42);
});

for await (const event of on(ee, 'foo')) {
  // The execution of this inner block is synchronous and it
  // processes one event at a time (even with await). Do not use
  // if concurrent execution is required.
  console.log(event); // prints ['bar'] [42]
}
// Unreachable hereconst { on, EventEmitter } = require('node:events');

(async () => {
  const ee = new EventEmitter();

  // Emit later on
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo')) {
    // The execution of this inner block is synchronous and it
    // processes one event at a time (even with await). Do not use
    // if concurrent execution is required.
    console.log(event); // prints ['bar'] [42]
  }
  // Unreachable here
})();

Returns an AsyncIterator that iterates eventName events. It will throw if the EventEmitter emits 'error'. It removes all listeners when exiting the loop. The value returned by each iteration is an array composed of the emitted event arguments.

An <AbortSignal> can be used to cancel waiting on events:

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ac = new AbortController();

(async () => {
  const ee = new EventEmitter();

  // Emit later on
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo', { signal: ac.signal })) {
    // The execution of this inner block is synchronous and it
    // processes one event at a time (even with await). Do not use
    // if concurrent execution is required.
    console.log(event); // prints ['bar'] [42]
  }
  // Unreachable here
})();

process.nextTick(() => ac.abort());const { on, EventEmitter } = require('node:events');

const ac = new AbortController();

(async () => {
  const ee = new EventEmitter();

  // Emit later on
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo', { signal: ac.signal })) {
    // The execution of this inner block is synchronous and it
    // processes one event at a time (even with await). Do not use
    // if concurrent execution is required.
    console.log(event); // prints ['bar'] [42]
  }
  // Unreachable here
})();

process.nextTick(() => ac.abort());