javascript - 使用构造函数创建一个新对象并在 javascript 中调用函数

Question

我在使用这段代码时遇到了一些问题:

window.onload = function() {
// Make a new method isLeapYear and accept the date argument.
Date.prototype.isLeapYear = function(date) {
    if(date.getFullYear() % 4 != 0) {
        return false;
    } else if(date.getFullYear() % 100 != 0) {
        return true;
    } else if(date.getFullYear() % 400 != 0) {
        return false;
    } else {
        return true;
    }
}


// Make a new method daysInMonth and accept the date argument.
Date.prototype.daysInMonth = function(date) {
    if(date.getMonth() === 0 || date.getMonth() === 2 || date.getMonth() === 4 || date.getMonth() === 6 || date.getMonth() === 7 || date.getMonth() === 9 || date.getMonth() === 11) {
        return "31";
    } else if(date.getMonth() === 3 || date.getMonth() === 5 || date.getMonth() === 8 || date.getMonth() === 10) {
        return "30";
    } else if(date.getMonth() === 1) {
        if(date.isLeapYear(date) === true) {
            return "29";
        } else {
            return "28";
        }
    }
}

// Make a new method ageInYears and accept the date argument.
Date.prototype.ageInYears = function(date) {
    return Math.floor((new Date() - date) / 1000 / 60 / 60 / 24 / 365.2595);
}

function Person(firstname, lastname, mi, birthdate) {
    this.firstname = firstname;
    this.lastname = lastname;
    this.mi = mi;
    this.birthdate = birthdate;
    this.age = this.birthdate.ageInYears(this.birthdate);
}

Person.prototype.setBirthdate = function(month,day,year) {
        currentYear = new Date().getFullYear();
        currentMonth = new Date().getMonth();
        currentDay = new Date().getDate();

        if(month > currentMonth && day > currentDay && year > currentYear || month > currentMonth && year > currentYear) {
            return "Month/Day/Year not valid.";
        } else {
            return (new Date(year, month, day)); 
        }
}

var newGuy = new Person("New", "Guy", "J",  Person.setBirthdate(5,7,1989));
}

我收到错误“未捕获类型错误:未定义不是函数 person.js:59”这就是说 undefined 不是新 Person 对象上的函数。怎么会？我被难住了一段时间，有人可以帮我吗？

Answer 1

您的 setBirthdate 方法相当静态，并且不会修改调用它的实例。它不应该放在原型(prototype)上，并且以不同的方式命名。

function Person(firstname, lastname, mi, birthdate) {
    this.firstname = firstname;
    this.lastname = lastname;
    this.mi = mi;
    this.setBirthdate(birthdate); // call prototype methods on the instance
}
Person.prototype.setBirthdate = function(birthdate) {
    this.birthdate = birthdate;
    this.age = this.birthdate.ageInYears(this.birthdate);
};

// place the static validation function on the constructor itself:
Person.makeBirthdate = function(month,day,year) {
    var currentYear = new Date().getFullYear(),
        currentMonth = new Date().getMonth(),
        currentDay = new Date().getDate();

    if (month > currentMonth && day > currentDay && year > currentYear || month > currentMonth && year > currentYear) {
        throw "Month/Day/Year not valid.";
    } else {
        return new Date(year, month, day); 
    }
}
// where you can call it before having instantiated the `newGuy`
var newGuy = new Person("New", "Guy", "J",  Person.makeBirthdate(5,7,1989));