js对象继承

　一般继承时出现的问题

    function people(name,sex){
      this.name=name;
      this.sex=sex;
    }
    people.prototype.showname=function(){
      alert(this.name);
    }
    function student(name,sex,job){
      people.call(this,name,sex);
      this.job=job;
    }
    student.prototype = people.prototype;//对象赋给对象，就会出现对象的引用，如果子类原型添加一个方法，父类就会受影响
    var p1=new people('jack',32);
    var s1=new student('jenny',24,'student');
    console.log(p1);
    console.log(s1);

拷贝继承：通用型的，有new或无new的时候都可以

  function people(name,sex){
      this.name=name;
      this.sex=sex;
    }
    people.prototype.showname=function(){
      alert(this.name);
    }
    function student(name,sex,job){
      people.call(this,name,sex);//属性继承：调用父类的构造函数
      this.job=job;
    }

    extend(student.prototype,people.prototype);//拷贝继承,利用for in 实现方法的继承
    student.prototype.showjob=function(){
      alert();
    }
    function extend(obj1,obj2){
      for (var attr in obj2) {
        obj1[attr]=obj2[attr];
      }
    }
    var p1=new people('jack',32);
    var s1=new student('jenny',24,'student');

    console.log(p1);
    console.log(s1);

 类式继承：带new构造函数

function Aaa(){
    this.name=[2,3,4];
}
Aaa.prototype.showname=function(){
    alert(this.name);
}
function Bbb(){
    Aaa.call(this);
}
var F= function(){};
F.prototype=Aaa.prototype;
Bbb.prototype=new F();
Bbb.prototype.constructor=Bbb;
var b1=new Bbb();
b1.name.push(5);
var b2=new Bbb();
alert(b2.showname);

原型继承：无new的对象

var a = {name: '小明'};
var b = clone(a);
b.name='小青';
alert(a.name);
function clone(obj){
    var F =function(){};
    F.prototype=obj;
    return new F();
}