js 用 hasOwnProperty() 判定属性是来自该对象成员，还是原型链

var People=function(){
this.name='liujinyu';
};

People.prototype={
age:24,
add:function(){},
}

var p1 = new People();

for(n in p1){
document.write(n+":"+p1
+" / "+p1.hasOwnProperty(n));
document.write("<br />");
}
　　//name true
　　//age false
　　//add false