异步 VS 同步

EventEmitter 按照注册的顺序同步地调用所有监听器。 这确保了事件的正确排序，并有助于避免竞争条件和逻辑错误。 在适当的时候，监听器函数可以使用 setImmediate() 或 process.nextTick() 方法切换到异步的操作模式：

import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
  setImmediate(() => {
    console.log('this happens asynchronously');
  });
});
myEmitter.emit('event', 'a', 'b');const EventEmitter = require('node:events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
  setImmediate(() => {
    console.log('this happens asynchronously');
  });
});
myEmitter.emit('event', 'a', 'b');

The EventEmitter calls all listeners synchronously in the order in which they were registered. This ensures the proper sequencing of events and helps avoid race conditions and logic errors. When appropriate, listener functions can switch to an asynchronous mode of operation using the setImmediate() or process.nextTick() methods:

import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
  setImmediate(() => {
    console.log('this happens asynchronously');
  });
});
myEmitter.emit('event', 'a', 'b');const EventEmitter = require('node:events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
  setImmediate(() => {
    console.log('this happens asynchronously');
  });
});
myEmitter.emit('event', 'a', 'b');