[Node][Unit33] 模擬 Event Emitter

app.js

const Emitter = require('./emitter')

let emtr = new Emitter()

emtr.on('greet', function () {
  console.log('Somewhere, someone said hello')
})

emtr.on('greet', function () {
  console.log('A greeting occurred')
})

console.log('Hello')
emtr.emit('greet')

mitter.js

function Emitter () {
  this.events = {}
}

Emitter.prototype.on = function (type, listener) {
  this.events[type] = this.events[type] || []
  this.events[type].push(listener)
}

/*
{
  'onSaveFile': [function(){}, function(){}]
}
*/

Emitter.prototype.emit = function (type) {
  if (this.events[type]) {
    this.events[type].forEach(listener => {
      listener()
    })
  }
}

module.exports = Emitter