修改对象的原型不起作用

时间:2013-11-03 15:10:11

标签: javascript prototype prototype-programming

我一直试图弄清楚为什么这不起作用。如果有人可以帮助我,我将不胜感激!

function Person(name, age) {
    this.name = name;
    this.age = age;
    var ageInTenYears = age + 10; 
    this.sayNameAndAge = function() {
      console.log(name + age);
    }
}

Person.prototype.sayAge = function() {
   console.log(this.age); 
}

Person.prototype = { 
    sayName : function(){
       console.log(this.name); 
    },
    sayNameAfterTimeOut : function(time) {
       setTimeout(this.sayName, time);
    },
    sayAgeInTenYears : function() { 
       console.log(ageInTenYears);
    } 
}

var bob = new Person('bob', 30); 
bob.sayName();

我收到此错误:

  Uncaught TypeError: Object #<Object> has no method 'sayAge' 

3 个答案:

答案 0 :(得分:7)

您正在通过

覆盖整个原型
Person.prototype = { /* ... */ };

表示您之前添加的sayAge方法再次丢失。要么颠倒这些作业的顺序,要么将sayAge移到另一个作业中。

答案 1 :(得分:3)

使用Person.prototype = { … };,您将重写prototype对象,即用一个全新的对象替换旧对象。 Cou可以做到这一点,但确保你事先没有定义任何方法(就像你上面的.sayAge一样)。

答案 2 :(得分:0)

代码有几个问题,我在纠正它的地方做了一些评论。如果您有任何疑问,可以对此答案发表评论:

function Person(name, age) {
    this.name = name;
    this.age = age;
    //var ageInTenYears = age + 10; //<--Why var, you can't
    // use this anywhere but in the Person constuctor body
    this.ageInTenYears=age+10;
}

Person.prototype = { 
    sayName : function(){
       console.log(this.name); 
    },
    sayNameAfterTimeOut : function(time) {
       // check out this link about what this can be
       // https://stackoverflow.com/a/19068438/1641941
       var me=this;
       setTimeout(function(){
         me.sayName();
       }, time);
    },
    sayAgeInTenYears : function() { 
      // you defined it as var so cannot use
      // ageInTenYears outside the constructor body
      //console.log(ageInTenYears);
      console.log(this.ageInTenYears);
    } 
};
Person.prototype.sayAge = function() {
   console.log(this.age); 
};
Person.prototype.sayNameAndAge = function() {
  console.log(this.name + this.age);
};
//just for good measure, someone may do
// Person.prototype.haveBaby=function(){
//   return new this.constructor();
Person.prototype.constructor=Person;

var bob = new Person('bob', 30); 
bob.sayName();

更多关于原型,继承/混合,覆盖和调用超级:https://stackoverflow.com/a/16063711/1641941