//定义一个构造函数
 function People(name,age){
  this.name=name;
  this.age=age;
  this.dothings=function(){
   retrun this.name+this.age;
   }
 }
 var people1 = new People("panda1",25);
 var people2 = new People("panda2",26);
 alert(people1.name==people2.name) //false

 People.prototype={
 constructor:People //强制指向People
  name:"panda",
  age:25,
  dothings:function(){
   return this.name+this.age;
  }
}
var people = new People();
alert(people.constructor); //function People(){}

//声明一个构造函数
 function People(){}
 //在原型添加属性
 People.prototype.name="panda";
 People.prototype.age=25;
 people.prototype.dothings=function(){
  return this.name+this.age;
 }  
 //实例化构造函数
 var people1 = new People();
 var people2 = new People();
 alert(people1.name==perople2.name) //true 因为都是原型里的方法，它们的地址是共享的，大家都来自同一地方。

var people = new People();
people.name="bear";
alert(people.name); //bear
alert(people1.name); //panda