函数不应该返回 NaN

Question

为什么 myTodos.meetDone() 函数返回 Nan？ 它当然是 js，我只是定义了一个名为 myTodos 的对象，我只想打印 console.log() 结果。

let myTodos = {
    day: 'Monday',
    meetings: 0,
    meetDone: 0,


    addMeeting: function (num) {
        this.meetings = this.meetings + num;
    },
    meetDone: function (num) {
        this.meetDone = this.meetDone - num;
    },
    resetDay: function () {
        this.meetings = 0;
        this.meetDone = 0;
    },
    report: function () {
        let meetleft = this.meetings + this.meetDone;
        return `Yo have ${meetleft} meeting for today!`;
    },
}

myTodos.addMeeting(2);
myTodos.addMeeting(5);
myTodos.meetDone(23);

console.log(myTodos);

console.log(myTodos.report());

第一个 console.log 用于调试 为什么它会返回 Nan 我不明白这个！！！！

Answer 1

正如@AndrewBone 在他的评论中已经提到的，您的对象有两个属性，称为meetDone。后一个覆盖第一个，因此当您添加 this.meetings + this.meetDone 时，您正在向 Number 添加一个函数，这会导致显示 NaN。更改其中一个属性的名称，meetingDone 比meetDone IMO 更具描述性

let myTodos = {
    day: 'Monday',
    meetings: 0,
    meetDone: 0,


    addMeeting: function (num) {
        this.meetings = this.meetings + num;
    },
    meetingDone: function (num) {
        this.meetDone = this.meetDone - num;
    },
    resetDay: function () {
        this.meetings = 0;
        this.meetDone = 0;
    },
    report: function () {
        let meetleft = this.meetings + this.meetDone;
        return `Yo have ${meetleft} meeting for today!`;
    },
}

myTodos.addMeeting(2);
myTodos.addMeeting(5);
myTodos.meetingDone(23);

console.log(myTodos);

console.log(myTodos.report());