How to implement an observer with coffeescript - coffeescript

Question

I try to implement the observer pattern in coffeescript like wikipedia observer pattern. How can this be done with coffeescript?

Answer 1

Create a class like this:
class Observer
constructor: () ->
#subscribers = {}
notify: (to, arg...) ->
if #subscribers[to]
for cb in #subscribers[to].callback
try
cb.apply #,[to].concat arg
catch err
console.log to+" "+(arg?.join ', ')+": "+err
subscribe: (to, cb) ->
if #subscribers[to]==undefined || #subscribers[to].callback.size==0
#subscribers[to]={'callback':[cb]}
else
#subscribers[to].callback.push cb if cb not in #subscribers[to].callback
unsubscribe: (to, cb) ->
#subscribers[to]?.callback.splice #subscribers[to].callback.indexOf(cb), 1
How to use
### Define subscriber ###
class SubscriberA
onEvent: (item) ->
console.log item
class SubscriberB
onEvent: (item) ->
console.log item
class SubscriberC
onEventTypeA: (item) ->
console.log "EventTypeA: "+item
onEventTypeB: (item) ->
console.log "EventTypeB: "+item
class SubscriberD
onEventTypeA: (item,arg="23 is default") ->
console.log item+" "+arg
onEventTypeB: (item,arg...) ->
console.log item + " with: "
for a in arg
console.log a
### Create observer ###
myO = new Observer()
### Create subscribing objects
In real live this would be your objects that will have to provide a function that handels notifications. Within this example they are called onEventXYZ
###
subscriptionOfA = new SubscriberA()
subscriptionOfB = new SubscriberB()
subscriptionOfC = new SubscriberC()
subscriptionOfD = new SubscriberD()
console.log ": Subscribe Peter once and Paul twice"
myO.subscribe "Peter", subscriptionOfA.onEvent
myO.subscribe "Paul", subscriptionOfA.onEvent
myO.subscribe "Paul", subscriptionOfA.onEvent
console.log ": Notify Peter and Paul"
myO.notify "Peter"
myO.notify "Paul"
console.log ": Paul is only notified once as duplicate subscriptions are ignored while subscribe"
console.log ": Subscribe Paul with a different subscriber"
myO.subscribe "Paul", subscriptionOfB.onEvent
console.log ": Notify Peter and Paul"
myO.notify "Peter"
myO.notify "Paul"
console.log ": Paul is notified twice as two different subscriptions are subscribed"
console.log "\n: Unsubscribe Peter"
myO.unsubscribe "Peter"
console.log ": Notify Peter and Paul"
myO.notify "Peter"
myO.notify "Paul"
console.log "\n: Not subscribed items will be ignored at notify"
console.log ": Notify Bob"
myO.notify "Bob"
console.log "\n: You may use multiple eventHandler in your subsribers"
myO.subscribe "Mary", subscriptionOfC.onEventTypeA
myO.subscribe "Jane", subscriptionOfC.onEventTypeB
console.log ": Notify Mary and Jane"
myO.notify "Mary"
myO.notify "Jane"
console.log "\n: You may use arguments with your eventHandler"
myO.subscribe "Laurel", subscriptionOfD.onEventTypeA
myO.subscribe "Hardy", subscriptionOfD.onEventTypeB
console.log ": Notify Laurel without argument"
myO.notify "Laurel"
console.log ": Notify Laurel with argument"
myO.notify "Laurel", 42
console.log ": Notify Hardy with multiple arguments"
myO.notify "Hardy", "Argument String",1,2,3,['a','b']