Stu emitter class

Illiustrating a problem with mutating data set on line 24.

by andfinally

JavaScript

function getSubscriptionSet (emitter, message) {
  if (!emitter.subscriptions[message]) {
    emitter.subscriptions[message] = []
  }
  return emitter.subscriptions[message]
}

class Emitter {
  constructor () {
    this.subscriptions = {}
  }

  clone () {
    return {
      emit: this.emit.bind(this),
      off: this.off.bind(this),
      on: this.on.bind(this),
      once: this.once.bind(this)
    }
  }

  emit (message, ...data) {
    console.log('NUMBER OF EMITS TO EMIT: ', getSubscriptionSet(this, message).length)
    getSubscriptionSet(this, message).forEach(callback => {
      console.log('EMITTING')
      callback(...data)
    })
  }

  off (message, callback) {
    let set = getSubscriptionSet(this, message)
    if (callback) {
      let index = set.indexOf(callback)
      if (index !== -1) set.splice(index, 1)
    } else {
      set.length = 0
    }
  }

  on (message, callback) {
    getSubscriptionSet(this, message).push(callback)
  }

  once (message, callback) {
    console.log('CREATE NEW EMITTER: ', message)
    let subscription = (...data) => {
      this.off(message, subscription)
      callback(...data)
    }
    this.on(message, subscription)
  }
}

const tag = () => {}

const emitter = new Emitter()

emitter.once('bidding finished', () => {
	tag()
})
emitter.once('bidding finished', () => {
	tag()
})
emitter.once('bidding finished', () => {
	tag()
})
emitter.once('bidding finished', () => {
	tag()
})
emitter.once('bidding finished', () => {
	tag()
})
emitter.once('bidding finished', () => {
	tag()
})
emitter.once('bidding finished', () => {
	tag()
})

emitter.emit('bidding finished')