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");