Event

const EventEmitter = require('events');

class MyEmitter extends EventEmitter {}

const myEmitter = new MyEmitter();
myEmitter.on('event', function(a, b) {
  console.log(a, b, this);
  // 打印:
  //   a b MyEmitter {
  //     domain: null,
  //     _events: { event: [Function] },
  //     _eventsCount: 1,
  //     _maxListeners: undefined }
});
myEmitter.emit('event', 'a', 'b');

// 只执行一次
const myEmitter = new MyEmitter();
let m = 0;
myEmitter.once('event', () => {
  console.log(++m);
});
myEmitter.emit('event');
// 打印: 1
myEmitter.emit('event');
// 忽略

// 移除事件监听 removeListener(eventName, listener) 和 removeAllListeners([eventName])
const callback = (stream) => {
  console.log('有连接！');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);