Extjs的静态成员

Ext.define('Computer',{ 
           statics:{ 
               instanceCount:0, 
               factory:function(brand){ 
               // 'this' in static methods refer to the class itself 
               return new this({brand: brand}); } 
               },  
           config:{ brand:null },
           constructor:function(config){ 
               this.initConfig(config);  
               // the 'self' property of an instance refers to its class 
               this.self.instanceCount++;  
                return this; 
               } 
});  

var dellComputer=Computer.factory('Dell'); 
var appleComputer=Computer.factory('Mac');  
alert(appleComputer.getBrand());// using the auto-generated getter to get the value of a config property. Alerts "Mac"  
alert(Computer.instanceCount);// Alerts "2"