ExtJS 4.x中如何定义类和使用类

Ext.define('My.sample.Person', {     name: 'Unknown',       constructor: function(name) {        if (name) {          this.name = name;         }          return this;     },      eat: function(foodType) {           alert(this.name + " is eating: " + foodType);         return this;    } });   var aaron = Ext.create('My.sample.Person', 'Aaron');     aaron.eat("Salad"); // alert("Aaron is eating: Salad");