使用 Javascript returns undefined 导出函数

Question

作为前言；我大约 3 天前开始学习 Javascript，所以我对某些事情的要求的理解并不完全。

所以，我有一个程序，我是运行，它使用时钟来制作带有时间戳的文件夹、文件和日志。但是当我从函数外部调用时间时它只是 returns undefined @ undefined:undefined:NaN 而在函数内部它 returns 时间就像正常的 10/2/2019 @ 11:6:45

function updateClock() {

    var currentdate = new Date();
    var day = currentdate.getDate();
    var month = currentdate.getMonth() + 1;
    var year = currentdate.getFullYear();
    this.date = " " + day + "/"
        + month + "/"
        + year;
    this.h = currentdate.getHours();
    this.m = currentdate.getMinutes();
    this.s = currentdate.getSeconds();
}

updateClock.prototype.run = function () {
    setInterval(this.update.bind(this), 1000);
};

updateClock.prototype.update = function () {
    this.updateTime(1);

    var time = " @ "
        + this.h + ":"
        + this.m + ":"
        + this.s;
    var datetime = this.date + time;
    console.log(datetime);
    return datetime;
};

updateClock.prototype.updateTime = function (secs) {
    this.s += secs;
    if (this.s >= 60) {
        this.m++;
        this.s = 0;
    };
    if (this.m >= 60) {
        this.h++;
        this.m = 0;
    };
    if (this.h >= 24) {
        this.day++;
        this.h = 0;
    }
};

var newclock = new updateClock();
newclock.run();




var timedate = updateClock.prototype.update();
console.log(timedate)

做什么以及如何修复？谢谢，我很感激！

Answer 1

您应该在 class 而不是 constructor 的实例上调用 update。

function updateClock() {

    var currentdate = new Date();
    var day = currentdate.getDate();
    var month = currentdate.getMonth() + 1;
    var year = currentdate.getFullYear();
    this.date = " " + day + "/"
        + month + "/"
        + year;
    this.h = currentdate.getHours();
    this.m = currentdate.getMinutes();
    this.s = currentdate.getSeconds();
}

updateClock.prototype.run = function () {
    setInterval(this.update.bind(this), 1000);
};

updateClock.prototype.update = function () {
    this.updateTime(1);

    var time = " @ "
        + this.h + ":"
        + this.m + ":"
        + this.s;
    var datetime = this.date + time;
    console.log(datetime);
    return datetime;
};

updateClock.prototype.updateTime = function (secs) {
    this.s += secs;
    if (this.s >= 60) {
        this.m++;
        this.s = 0;
    };
    if (this.m >= 60) {
        this.h++;
        this.m = 0;
    };
    if (this.h >= 24) {
        this.day++;
        this.h = 0;
    }
};

var newclock = new updateClock();
newclock.run();




var timedate = newclock.update();
console.log(timedate)

使用 Javascript returns undefined 导出函数

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