为什么这个代码返回NaN

只需在随机后添加（）

var deal = function() {
    var suit = Math.floor(Math.random() * 4 + 1);
    var number = Math.floor(Math.random() * 13 + 1);
    return new Card(number, suit);
}; 

你不应该打电话给吗

console.log(card1.getSuit());

您遇到了一些复合问题，但获得NaN的原因是使用了随机函数。请在对方法/函数的所有调用之后包含()。

对Card类进行了其他更改。this.将变量分配给该类实例。功能也是如此。因此，这将改变作为方法调用getSuit()的方式。它以前工作过，因为您的getSuit（）正被放入全局命名空间中。

function Card(num, suit){
    this.num = num; 
    this.suit = suit;
    this.getSuit = function(){
        return suit; 
    }; 
    this.getNumber = function(){
        return num; 
    };
    this.getValue = function(card){
        if (card > 10){
            return 10; 
        }else if (card === 1){
            return 11; 
        }else{
            return card; 
        }
    };
}
var deal = function(){
    var suit = Math.floor(Math.random() * 4 + 1);
    var number = Math.floor(Math.random() * 13 + 1);
    return new Card(number, suit); 
}; 

// examples of the deal function in action
var card1 = deal();
var card2 = deal();
console.log(card1.getSuit());

更改：

var num = num; 
var suit = suit;

至

this.num = num; 
this.suit = suit;

等等。

此版本保留了私有变量的使用。请注意，函数参数自动是私有变量，因此不需要重新声明它们。

function Card(num, suit) {
    this.getSuit = function() {
        return suit;
    }; 
    this.getNumber = function() {
        return num;
    };
    this.getValue = function() {
        if (num > 10)
            return 10;
        if (num == 1)
            return 11;
        return num;
    };
}

试试这个：

// Make your card constructor again here, but make sure to use private 
// variables!
function Card(num, suit){
    // NOTE: "this."
    this.num = num;
    this.suit = suit;
    this.getSuit = function(){
        return this.suit;
    };
    this.getNumber = function(){
        return this.num;
    };
    this.getValue = function(card){
        if (card > 10){
            return 10;
        }else if (card === 1){
            return 11;
        }else{
            return card;
        }
    };
}
// Make a deal function here.  It should return a new card with a suit
// that is a random number from 1 to 4, and a number that is a random
// number between 1 and 13   
var deal = function(){
    // NOTE: Math.random()
    var suit = Math.floor(Math.random() * 4 + 1);
    var number = Math.floor(Math.random() * 13 + 1);
    return new Card(number, suit);
};
// examples of the deal function in action
var card1 = deal();
var card2 = deal();
// NOTE: card1.getSuit()
console.log(card1.getSuit());

您需要解决三个独立的问题：

1. Math.random()上需要parens
2. 你需要像这样叫getSuit() card1.getSuit()，而不是你当时是怎么做的
3. 您需要实际使getSuit、getNumber和getValue成为Card对象的方法。正如您迄今为止所声明的，它们只是Card构造函数内部的局部函数，不能从该构造函数外部调用

有两种常见的方法可以使这些函数成为方法。一种是将它们分配给Card原型对象。另一种是将它们分配给构造函数中的this。

下面是将它们分配给原型对象的样子：

function Card(num, suit){
    this.num = num; 
    this.suit = suit;
}
Card.prototype = {
     getSuit: function() {
         return suit;
     },
     getNumber: function() {
         return num;
     },
     getValue: function(card) {
        if (card > 10){
            return 10; 
        }else if (card === 1){
            return 11; 
        }else{
            return card; 
        }
    }
};
// Make a deal function here.  It should return a new card with a suit
// that is a random number from 1 to 4, and a number that is a random
// number between 1 and 13
var deal = function(){
    var suit = Math.floor(Math.random() * 4 + 1);
    var number = Math.floor(Math.random() * 13 + 1);
    return new Card(number, suit); 
}; 

// examples of the deal function in action
var card1 = deal();
var card2 = deal();
console.log(card1.getSuit());

如果你想让num和suit保持私有变量，那么你必须在Card内部定义这样的方法：

// Make your card constructor again here, but make sure to use private
// variables!
function Card(num, suit){
    var num = num; 
    var suit = suit;
    this.getSuit = function(){
        return suit; 
    }; 
    this.getNumber = function(){
        return num; 
    };
    this.getValue = function(card){
        if (card > 10){
            return 10; 
        }else if (card === 1){
            return 11; 
        }else{
            return card; 
        }
    };
}
// Make a deal function here.  It should return a new card with a suit
// that is a random number from 1 to 4, and a number that is a random
// number between 1 and 13
var deal = function(){
    var suit = Math.floor(Math.random() * 4 + 1);
    var number = Math.floor(Math.random() * 13 + 1);
    return new Card(number, suit); 
}; 

// examples of the deal function in action
var card1 = deal();
var card2 = deal();
console.log(card1.getSuit());