继承方法-->一级一级继承

Grand.prototype.lastName = 'ji';
function Grand(){};
var grand = new Grand();
Father.prototype = grand;
function Father(){
      this.name = 'hehe';
};
var father = new Father();
Son.prototype = father;
function Son(){
      this.name = 'klkx'
};
var son = new Son();
console.log(son);

缺点没有必要的属性也一并继承了