design-pattern/src/observer.js

Javascript design patterns for both browser and Node.js

(function(exports){

	exports.createSubject = function(){
		return new Subject();
	};

	var Subject = function(){
	  this.observers = new ObserverList();
	};

	Subject.prototype.addObserver = function( observer ){
	  this.observers.add( observer );
	};

	Subject.prototype.removeObserver = function( observer ){
	  this.observers.removeAt( this.observers.indexOf( observer, 0 ) );
	};

	Subject.prototype.notify = function( context ){
	  var observerCount = this.observers.count();
	  for(var i=0; i < observerCount; i++){
	    this.observers.get(i).update( context );
	  }
	};

	var ObserverList = function(){
	  this.observerList = [];
	};

	ObserverList.prototype.add = function( obj ){
	  return this.observerList.push( obj );
	};

	ObserverList.prototype.count = function(){
	  return this.observerList.length;
	};

	ObserverList.prototype.get = function( index ){
	  if( index > -1 && index < this.observerList.length ){
	    return this.observerList[ index ];
	  }
	};

	ObserverList.prototype.indexOf = function( obj, startIndex ){
	  var i = startIndex;
	  while( i < this.observerList.length ){
	    if( this.observerList[i] === obj ){
	      return i;
	    }
	    i++;
	  }
	  return -1;
	};

	ObserverList.prototype.removeAt = function( index ){
	  this.observerList.splice( index, 1 );
	};

}(typeof exports === 'undefined' ? this.observerPattern = {} : exports));