javascript - 为什么这会返回 undefined - javascript

Question

我对 js 很陌生。如果这听起来很愚蠢，我很抱歉。但是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:

25岁年龄如下undefined

Answer 1

因为你不返回任何东西。