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

• emitter <EventEmitter>

• eventName <string> | <symbol> 正在监听的事件的名称

  ¥eventName <string> | <symbol> The name of the event being listened for

• options <Object>

  • signal <AbortSignal> 可用于取消等待事件。

    ¥signal <AbortSignal> Can be used to cancel awaiting events.

  • close <string[]> 将结束迭代的事件的名称。

    ¥close <string[]> Names of events that will end the iteration.

  • highWaterMark <integer> 默认值：Number.MAX_SAFE_INTEGER 高水位线。每当缓冲的事件大小高于它时，触发器就会暂停。仅在实现 pause() 和 resume() 方法的触发器上受支持。

    ¥highWaterMark <integer> Default: Number.MAX_SAFE_INTEGER The high watermark. The emitter is paused every time the size of events being buffered is higher than it. Supported only on emitters implementing pause() and resume() methods.

  • lowWaterMark <integer> 默认值：1 低水位线。每当缓冲的事件大小低于它时，触发器就会恢复。仅在实现 pause() 和 resume() 方法的触发器上受支持。

    ¥lowWaterMark <integer> Default: 1 The low watermark. The emitter is resumed every time the size of events being buffered is lower than it. Supported only on emitters implementing pause() and resume() methods.

• 返回：<AsyncIterator> 迭代 emitter 触发的 eventName 事件

  ¥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
})();拷贝

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。

¥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.

<AbortSignal> 可用于取消对事件的等待：

¥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());拷贝