added observer pattern

Author: AnjanishKumar

pattern/observer-pattern.js

@@ -0,0 +1,94 @@
+// build the Subject base class
+var window = window || null;
+var Subject = ( function( window, undefined ) {
+
+  function Subject() {
+    this._list = [];
+  }
+
+  // this method will handle adding observers to the internal list
+  Subject.prototype.observe = function observeObject( obj ) {
+    console.log( 'added new observer' );
+    this._list.push( obj );
+  };
+ 
+  //this method will remove an existing observer form internal list	 
+  Subject.prototype.unobserve = function unobserveObject( obj ) {
+    for( var i = 0, len = this._list.length; i < len; i++ ) {
+      if( this._list[ i ] === obj ) {
+        this._list.splice( i, 1 );
+        console.log( 'removed existing observer' );
+        return true;
+      }
+    }
+    return false;
+  };
+  
+  Subject.prototype.notify = function notifyObservers() {
+    var args = Array.prototype.slice.call( arguments, 0 );
+    for( var i = 0, len = this._list.length; i < len; i++ ) {
+      this._list[ i ].update(args );
+    }
+  };
+
+  return Subject;
+
+} )( window );
+
+// setup an object that fetchs stocks
+function StockGrabber() {
+  
+  var subject = new Subject();
+  
+  this.addObserver = function addObserver( newObserver ) {
+    subject.observe( newObserver );
+  };
+  
+  this.removeObserver = function removeObserver( deleteObserver ) {
+    subject.unobserve( deleteObserver );
+  };
+  
+  this.fetchStocks = function fetchStocks() {
+    // fake fetching the stocks
+    var stocks = {
+      aapl : 167.00,
+      goog : 243.67,
+      msft : 99.34
+    };
+    
+    // notify our observers of the stock change
+    subject.notify( stocks );
+  };
+  
+}
+
+// define a couple of different observers
+var StockUpdaterComponent = {
+  update : function() {
+    console.log( '"update" called on StockUpdater with: ', arguments );
+  }
+};
+var StockChartsComponent = {
+  update : function() {
+    console.log( '"update" called on StockCharts with: ', arguments );
+  }
+};
+
+// example usage
+var stockApp = new StockGrabber();
+
+//add the StockUpdaterComponent to observer list
+stockApp.addObserver( StockUpdaterComponent );
+stockApp.fetchStocks(); // console logs: "update" called on StockUpdaterComponent with...
+
+//add the StockChartsComponent to observer list
+stockApp.addObserver( StockChartsComponent );
+stockApp.fetchStocks(); // console logs: "update" called on StockUpdater with... "update" called on StockCarts with...
+
+//remove the stockUpdaterComponent form observer list
+stockApp.removeObserver( StockUpdaterComponent );
+stockApp.fetchStocks(); // console logs: "update" called on StockCharts with...
+
+//remove the stockChartsComponent form observer list
+stockApp.removeObserver( StockChartsComponent );
+stockApp.fetchStocks(); // does nothing; no observers