Understanding better Javascript OOP architecture [duplicate]

Answer 1

I think handleLocationChange is called from event triggering object that registers listeners but doesn't register the this context so when it's triggered you can't use this as it refers to handleLocationChange. To overcome this they have chosen to set a closure reference to this (=the self variable) and call other instance functions using self. Basically it's storing a value known at creation but not known when handleLocationChange is executing.

Here is some code showing the problem:

var eventSystem={
  events:{},
  add:function(eventname,fnCallback){
     if(!this.events[eventname]){
      this.events[eventname]=[];
     }
     this.events[eventname].push(fnCallback);
  },
  trigger:function(eventname){
    if(!this.events[eventname]){
      return;
    }
    var i=0;
    for(i=0;i

Here is how it's solved setting a closure reference

var eventSystem={
  events:{},
  add:function(eventname,fnCallback){
     if(!this.events[eventname]){
      this.events[eventname]=[];
     }
     this.events[eventname].push(fnCallback);
  },
  trigger:function(eventname){
    if(!this.events[eventname]){
      return;
    }
    var i=0;
    for(i=0;i

Here is a fix to the event system to take care of the this context:

var eventSystem={
  events:{},
  add:function(eventname,fnCallback,thisRef){
     if(!this.events[eventname]){
      this.events[eventname]=[];
     }
     this.events[eventname].push({
       "callback":fnCallback,//store the event handler
       "thisRef":thisRef//store the this context
     });
  },
  trigger:function(eventname){
    if(!this.events[eventname]){
      return;
    }
    var i=0;
    for(i=0;i

The pattern used above is not an event system (think it's pulisher subscriber) as an event usually get triggered on or invoked from an object (button, input, dialog) but in case of a more event system like implementation it would be easy to get the correct this context since you trigger the event on or from an instance (like myButton or myDialog).

See following code for event system like implementation:

var eventSystem={
  add:function(eventname,fnCallback){
     if(!this.events[eventname]){
      this.events[eventname]=[];
     }
     this.events[eventname].push(fnCallback);
  },
  //change in trigger as it's passing the event object now
  trigger:function(event){
    if(!this.events[event.type]){
      return;
    }
    var i=0;
    for(i=0;i

Not sure why Angular choose to "break" prototype by using closures as the examples show there are other alternatives. Maybe someone can explain that who is more familiar with Angular.