óCoffeeScript Cookbook

Observer Pattern


You have to notify some objects about an event happen


Use an Observer Pattern

class PostOffice
	constructor: () ->
		@subscribers = []
	notifyNewItemReleased: (item) ->
		subscriber.callback(item) for subscriber in @subscribers when subscriber.item is item
	subscribe: (to, onNewItemReleased) ->
		@subscribers.push {'item':to, 'callback':onNewItemReleased}

class MagazineSubscriber
	onNewMagazine: (item) ->
		alert "I've got new "+item

class NewspaperSubscriber
	onNewNewspaper: (item) ->
		alert "I've got new "+item

postOffice = new PostOffice()
sub1 = new MagazineSubscriber()
sub2 = new NewspaperSubscriber()
postOffice.subscribe "Mens Health", sub1.onNewMagazine
postOffice.subscribe "Times", sub2.onNewNewspaper
postOffice.notifyNewItemReleased "Times"
postOffice.notifyNewItemReleased "Mens Health"


Here you have an observer object (PostOffice) and observable objects (MagazineSubscriber, NewspaperSubscriber). To be notified about an event of publishing new periodical observable object should make subscription on PostOffice. Every of subscribed objects is stored internally in the PostOffice array of subscriptions. Every subscriber is notified on new concrete periodical is published.