为什么这会返回undefined -javascript

Question

我对js很新.如果这听起来很蠢,我很抱歉.但为什么下面的代码返回"undefined"

function NewPerson(name, age, sex){
    this.name = name;
    this.age = age;
    this.sex = sex;

    this.getName = function(){
        //alert(this.name);
        alert("The age is "+this.age);
    };

}

var obj1 = new NewPerson("Mark",25,"Male");
alert("The age is as follows "+obj1.getName());

//输出:

年龄为25岁.未定义年龄如下

Answer 1

因为你没有退货.