测试动态增多属性

function f(name,age){
	this.name=name;
	this.age=age;
	this.addAge=function(){alert("cheng")};
}
var p=new f("tom",12);
alert(p.name);
var s=new f("tom",16);
s.city="shandong";
alert(p.city);
alert(typeof(s.city));