观察者模式

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class EventEmitter {
  constructor () {
    this.handles = {}
  }
  on (name, cb) {
    if (!this.handles) this.handles = {}
    if (!this.handles[name]) this.handles[name] = []
    this.handles[name].push(cb)
  }

  emit (name, ...args) {
    if (this.handles[name]) {
      for (var i = 0; i < this.handles[name].length; i++) {
        this.handles[name][i](...args)
      }
    }
  }
}

let event = new EventEmitter()
event.on('say', function(name) {
  console.log('hello, ' + name)
})

event.emit('say', 'lilei')