js继承的问题

Question

在js中可以用对象冒充来实现继承机制,我做了个例子如下所示:function people(name,age){
this.name=name;
this.age=age;
this.sayHello=function(){
alert("Hello,"+this.name)
}
}
function student(name,age,grade,school){
this.people=people;
this.people(name,age)
this.grade=grade;
this.school=school;
}
var s=new student("小伟",25,"classI","中国大学");
s.sayHello()这样可以弹出"Hello,小伟",我修改了代码,如下所示：function people(name,age){
this.name=name;
this.age=age;
this.sayHello=function(){
alert("Hello,"+this.name)
}
}
function student(name,age,grade,school){
//this.people=people;
//this.people(name,age)
this.people=function(name,age){
this.name=name;
this.age=age;
this.sayHello=function(){
alert("Hello,"+this.name)
}
}
this.grade=grade;
this.school=school;
}
var s=new student("小伟",25,"classI","中国大学");
//s.people("然思维",25)
s.sayHello()这时再执行就不弹出了，直接报错,说s.sayHello()不是一个function,我想问下这是为什么？区别在哪里？

Answer 1

你这样写 让我很纠结
s.people.sayhello();这样试下

Answer 2

student 没有继承 people 

Answer 3

function people(name, age) {
    this.name = name;
    this.age = age;
}
people.prototype.sayHello = function() {
    alert("Hello," + this.name)
}
function student(name, age, grade, school) {
    this.name = name;
    this.age = age;
    this.grade = grade;
    this.school = school;
}student.prototype = new people();
student.prototype.getSchool = function() {
    alert(this.school);
};
var s = new student("小伟", 25, "classI", "中国大学");
s.sayHello();
s.getSchool();

Answer 4

楼上的通过原型对象方法继承是可以的，这里提供另外一种继承方法 function people(name,age){ 
this.name=name; 
this.age=age; 
this.sayHello=function(){ 
alert("Hello,"+this.name) 
} 
} 
function student(name,age,grade,school){ 
                // 利用函数的call()或者apply()方法也可以实现继承
people.call(this,name,age);
this.grade=grade; 
this.school=school; 
} 
var s=new student("小伟",25,"classI","中国大学"); 
s.sayHello()

Answer 5

我的理解是：
this.people=people;
this.people(name,age)
这样调用时，people定义里的this.sayHello里的this是指student对象this.people=function(name,age){
     this.name=name;
     this.age=age;
     this.sayHello=function(){
         alert("Hello,"+this.name)
     }
 }
这样调用时，this.sayHello里的this指的是this.people，所以应该是s.people.sayHello()感觉挺绕的……

Answer 6

我是5楼的
又想了一下，我在楼上说的不正确
实际上第二种方法不能用是在因为对象声明this.people只是赋了值，但是未被执行过，即是说在调用student.people之前，this.sayHello=function()...实际未执行
所以应该先执行s.people方法，再调用sayHello函数，即
s.people(s.name, s.age);
s.sayHello();

Answer 7

function student(name,age,grade,school){
    //this.people=people;
    //this.people(name,age)
    this.people=function(name,age){
        this.name=name;
        this.age=age;
        this.sayHello=function(){
            alert("Hello,"+this.name)
        }
    }
    this.people();
    this.grade=grade;
    this.school=school;
}
上面那段FUNCTION还没有没执行 只是被赋予了people
后面加句 this.people();应该就可以了

Answer 8

你这样写当然不能这样调用了，应该是s.people.sayHello();
当然你样就不是继承了，相当于重写

Answer 9

不知道楼主到底想怎样，其实用是可以用的啊。只是那个注释掉的应该取消注释。因为你的SayHello是在people函数里定义的，必须执行它才能有你这个SayHello。
<script type="text/javascript">function student(name,age,grade,school){
    //this.people=people;
    //this.people(name,age)
    this.people=function(name,age){
        this.name=name;
        this.age=age;
        this.sayHello=function(){
            alert("Hello,"+this.name)
        }
    }
    this.grade=grade;
    this.school=school;
}
var s=new student("小伟",25,"classI","中国大学");
s.people("然思维",25);
s.sayHello();</script>

Answer 10

或者这样：
<script type="text/javascript">
function student(name,age,grade,school){
    this.people=function(name,age){
        this.name=name;
        this.age=age;
        this.sayHello=function(){
            alert("Hello,"+this.name)
        }
    }
    this.people(name,age);
    this.grade=grade;
    this.school=school;
}
var s=new student("小伟",25,"classI","中国大学");
s.sayHello();</script>

Answer 11

这样写法其实和下面这种写法是一样的:function people(name,age){
    this.name=name;
    this.age=age;
    this.sayHello=function(){
        alert("Hello,"+this.name)
    }
}
function student(name,age,grade,school){
    this.people=people;
    this.people(name,age)
    this.grade=grade;
    this.school=school;
}
var s=new student("小伟",25,"classI","中国大学");
s.sayHello()this.pepole只是赋值但是没有执行,对象冒充其实和用call来继承一样,上面的写法等价于:function people(name,age){
    this.name=name;
    this.age=age;
    this.sayHello=function(){
        alert("Hello,"+this.name)
    }
}
function student(name,age,grade,school){
  people.call(this,name,age);
    this.grade=grade;
    this.school=school;
}
var s=new student("小伟",25,"classI","中国大学");
s.sayHello()

Answer 12

对象冒充的精髓在于this对象的替换
而javascript是动态执行的。所以写在闭包内的this并不认识外面的function
必须要执行下。才能把里面的this，动态链接到外面的this上。从而实现继承。
p.s.
我认为你的第一种对象冒充写法还是不完全
function people(name,age){
    this.name=name;
    this.age=age;
    this.sayHello=function(){
        alert("Hello,"+this.name)
    }
}
function student(name,age,grade,school){
    this.people=people;
    this.people(name,age);
    delete this.people;
    this.grade=grade;
    this.school=school;
}
var s=new student("小伟",25,"classI","中国大学");
s.sayHello();
这句话很重要，否则你的子类中会多一个this.people属性