原型继承、构造函数继承、组合继承法

原型继承function Person(name,sex){ this.name=name; this.sex=sex; this.friends = {lily:‘female’,lucy:‘female’}; this.showFriends=function(){ var str = ’’ for(i in this.friends){ str+=i +’ ‘+this.friends[i] +’,’; } console.log(‘my friends:’+str); }}Person.prototype.hello=function(){ console.log(‘hello:’+this.name);}var per1 = new Person(‘A’,‘male’);per1.hello();per1.showFriends();function Student(className){ this.class = className;}Student.prototype = new Person(‘B’,‘male’);//原型继承将子对象的原型对象指向父对象的实例 ； 缺点：不能由子对象像父对象传递参数，var stu1 = new Student(1);//不能由子对象像父对象传递参数，stu1.name=‘C’;stu1.hello();stu1.friends.C = ‘male’;//2、对于引用型的属性修改之后会印象其他的实例对象；stu1.showFriends();//2、对于引用型的属性修改之后会印象其他的实例对象；console.log(“stu1 instanceof Student: “);console.log(stu1 instanceof Student);console.log(“stu1 instanceof Person: “);console.log(stu1 instanceof Person);var stu2 = new Student(2);stu2.name=‘D’;stu2.hello();stu2.showFriends();//2、对于引用型的属性修改之后会印象其他的实例对象；console.log(“stu2 instanceof Student: “);console.log(stu2 instanceof Student);console.log(“stu2 instanceof Person: “);console.log(stu2 instanceof Person);缺点：1、不能由子对象像父对象传递参数，2、对于引用型的属性修改之后会印象其他的实例对象；构造函数继承//构造函数继承function Teacher(name,sex,type){ this.type=type; Person.call(this,name,sex);}var tea1 = new Teacher(‘E’,‘female’,‘数学’);//tea1.hello(); //报错没有继承到原型上的方法tea1.friends.F = ‘male’;tea1.showFriends();var tea2 = new Teacher(‘G’,‘male’,‘语文’);tea2.friends.H = ‘male’;tea2.showFriends();console.log(“tea2 instanceof Teacher: “)console.log(tea2 instanceof Teacher);console.log(“tea2 instanceof Person: “)console.log(tea2 instanceof Person);缺点：1、不能继承父对象原型上的方法 2、每次实例化对象会重新构建函数，浪费内存。组合继承法把父对象方法挂载到父类的原型对象上去，实现方法复用function Worker(name,sex,job){ this.job = job; Person.call(this,name,sex)}Worker.prototype = new Person();Worker.prototype.constructor = Worker;//原型的构造函数指向workervar wor1 = new Worker(‘I’,‘female’,‘程序员’);wor1.hello();wor1.friends.J = ‘male’;wor1.showFriends();