js-patterns/observerpattern.html at master · wizact/js-patterns · GitHub

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<html>
	<head>
		<title>Observer Pattern</title>
	</head>
	<body> Subject:
		<input type="checkbox" value="Subject" id="subjectCheckbox" />
		<div id="container">
			Observer(s):
		</div>
		<input type="button" value="Add Observer" id="addBtn" />


		<script type="text/javascript" src="jsutil/CollectionList.js"></script>
		<script type="text/javascript">

			// Subject::Starts
			function Subject(){
				this.observers = new CollectionList();
			}

			Subject.prototype.AddObserver = function ( observer ) {
				this.observers.Add( observer );
			};

			Subject.prototype.RemoveObserver = function ( observer ) {
				this.observers.RemoveAt( this.observers.IndexOf(observer) );
			};

			Subject.prototype.Notify = function ( context ) {
				var observerCount = this.observers.Count();
				for (var i =  0; i < observerCount; i++) {
					this.observers.Item(i).Update( context );
				}
			};
			// Subject::Ends

			// Observer:: Starts
			function Observer() {
				this.Update = function() {
					alert("Not implemented");
				};
			}
			// Observer:: Ends

			function extend( extension, obj) {
				for (var key in extension){
					obj[key] = extension[key];
					}
			}


			var subjectCh = document.getElementById("subjectCheckbox");
			var t = new Subject();
			extend(t , subjectCh );

			subjectCh["onclick"] = function () { this.Notify(this.checked); };

			var btn = document.getElementById("addBtn");
			btn["onclick"] = addNewObserver;

			function addNewObserver() {
				var container = document.getElementById("container");
				var element = document.createElement("input");
				element.type = "checkbox";

				extend(new Observer(), element);

				element.Update = function( value ) {
					this.checked = value;
				}

				subjectCh.AddObserver(element);
				container.appendChild(element);
			}
		</script>
	</body>
</html>