NaN顯然是一個數字，還是它？

Question

我在這裏遇到了一些麻煩。我檢查確保我的變量僅用數字定義，但代碼仍然是不是數字。任何人都知道我在做什麼錯了？下面

代碼：

//declare vars and/or constants 
var endString = "Total cost per night is $"; 
var viewCost; 
var discount; 

//input vars 
pplCount = prompt("How many people will be staying?"); 
discYes = prompt("Do you have an AAA discount?"); 
viewYes = prompt("Do you want a room with a view?"); 

//if variables 

if(pplCount === "1" || pplCount === "2" && discYes === "Yes" && viewYes === "Yes") { 
discount = 50 * 0.15; 
roomCost = 50; 
roomCost = +roomCost - discount + viewCost; 
viewCost = (+roomCost * 0.10); 
document.write(endString + roomCost); 
}else if(pplCount === "3" || pplCount === "4" && discYes === "Yes" && viewYes === "Yes") { 
discount = 60 * 0.10; 
roomCost = 60; 
roomCost = roomCost - discount + viewCost; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 
else if(pplCount === "5" || pplCount === "6" && discYes === "Yes" && viewYes === "Yes") { 
discount = 70 * 0.05; 
roomCost = 70; 
roomCost = roomCost - discount + viewCost; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 

else if(pplCount === "1" || pplCount === "2" && discYes === "No" && viewYes === "Yes") { 
discount = 50 * 0.15; 
roomCost = 50; 
roomCost = roomCost + viewCost; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 
else if(pplCount === "3" || pplCount === "4" && discYes === "No" && viewYes === "Yes") { 
discount = 60 * 0.10; 
roomCost = 60; 
roomCost = roomCost + viewCost; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 
else if(pplCount === "5" || pplCount === "6" && discYes === "No" && viewYes === "Yes") { 
discount = 70 * 0.05; 
roomCost = 70; 
roomCost = roomCost + viewCost; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 

else if(pplCount === "1" || pplCount === "2" && discYes === "No" && viewYes === "No") { 
discount = 50 * 0.15; 
roomCost = 50; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 
else if(pplCount === "3" || pplCount === "4" && discYes === "No" && viewYes === "No") { 
discount = 60 * 0.10; 
roomCost = 60; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 
else if(pplCount === "5" || pplCount === "6" && discYes === "No" && viewYes === "No") { 
discount = 70 * 0.05; 
roomCost = 70; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 

else if(pplCount === "1" || pplCount === "2" && discYes === "Yes" && viewYes === "No") { 
discount = 50 * 0.15; 
roomCost = 50; 
roomCost = roomCost - discount; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 
else if(pplCount === "3" || pplCount === "4" && discYes === "Yes" && viewYes === "No") { 
discount = 60 * 0.10; 
roomCost = 60; 
roomCost = roomCost - discount; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 
else if(pplCount === "5" || pplCount === "6" && discYes === "Yes" && viewYes === "No") { 
discount = 70 * 0.05; 
roomCost = 70; 
roomCost = roomCost - discount; 
viewCost = (roomCost * 0.10); 
document.write(endString + roomCost); 
} 

難道是因爲我定義兩次roomCost？

Answer 1

NaN就是你當Number操作提供了一個無效的結果（非數字）

像：

5 - "a" 
5 + NaN 
parseInt("a", 10) 
5 + undefined 

NaN在某種意義上有毒以使得具有NaN任何操作一個操作數也將返回NaN。找出你操作不當的地方。

看着你是代碼，我看到你正在使用字符串而不是數字。使用parseInt()將字符串轉換爲適當的Number。確保你驗證你的輸入，如果parseInt返回NaN給出錯誤。

Answer 2

var viewCost; // <---defined, but not assigned to 

roomCost = +roomCost - discount + viewCost; 
            ^^^^^^^^ 

在一次運行這個第一次，你只聲明的變量，但沒有分配給它尚未：

Answer 3

忽略你在這裏做什麼其他的頑皮的東西，你'在幾個地方使用viewCost而沒有首先定義它。 （這是非數字）

第幾行更改爲以下修復問題：

//declare vars and/or constants 
var endString = "Total cost per night is $"; 
var viewCost = 0; 
var discount = 0;