EventEmitter

观察者模式
addEventListener
removeEventListener

Event.js

const { EventEmitter } = require('events');
class Event extends EventEmitter {
  constructor() {
    super();
    setInterval(() => {
      this.emit('change', { price: Math.random() * 100})
    }, 2000)
  }
}
// 把底层的逻辑封装起来，
module.exports = Event;

index.js

const Event = require('./lib');
const jim = new Event();
jim.addListener('change', (res) => {
  if(res.price <= 80) {
    console.log('haha', res.price)
  }
})

setMaxListeners

EventEmitter如果添加了过多的监听器，Node.js觉得你有内存泄漏嫌疑，会抛出一个warning

setTimeout(() => {
  // geektime.setMaxListeners(200); 消除 warningn
  for (let i = 0; i < 100; i++) {
    event.on('channge', ({ res }) => {
    })
  }
}, 10000)