Javascript - 無法插入函數

Question

我想添加一個函數，如果用戶輸入非數字值，則將vticketqty設置爲0。我已經嘗試了一些東西，但是我的代碼從未正常工作，如果我添加了該功能，所以我顯然做錯了什麼。

這是我使用的功能：

function NaN(){ 
    if (isNaN(TicketQty)) TicketQty = 0; 
    } else { 
    return TicketQty 
} 

我不知道但其正確的，我不能完全肯定這個功能應該放在代碼中。這是我的JavaScript代碼。任何幫助，將不勝感激。

var vTicketType; 
var vTicketQty; 
var vTicketPrice; 
function calcTotal() { 
    vTicketType = prompt("Enter Ticket Type").toUpperCase(); 
    document.write("<br>"); 
    vTicketQty = prompt("Enter No. of Tickets"); 
    calcPrice(); 
    vTicketQty = parseInt(vTicketQty); 
    document.write("<br>"); 
    document.write("Type of Ticket:" + vTicketType); 
    document.write("<br>"); 
    document.write("Number of Tickets:" + vTicketQty); 
    document.write("<br>"); 
    var vTotalPayment =(vTicketPrice) * (vTicketQty); 
    if (vTotalPayment >0) { 
     document.write("Total Payment is: $" + vTotalPayment); 
     vTicketPrice = parseInt(vTicketPrice); 
    } else { 
     document.write("INVALID") 
    } 
} 



function calcPrice(){ 
    if (vTicketType == 'A') { 
     vTicketPrice = 50; 
    } else if (vTicketType == 'B') { 
     vTicketPrice = 30; 
    } else if (vTicketType == 'C'){ 
     vTicketPrice = 10; 
    } 
    else { 
     vTicketPrice = -1; 
    } 
} 

Answer 1

取而代之的是：

document.write("<br>"); 
vTicketQty = prompt("Enter No. of Tickets"); 
calcPrice(); 
vTicketQty = parseInt(vTicketQty); 
document.write("<br>"); 

試試這個。

document.write("<br>"); 
while (isNaN(vTicketQty)) { 
    vTicketQty = prompt("Enter No. of Tickets"); 
    calcPrice(); 
    vTicketQty = parseInt(vTicketQty); 
    if (isNaN(vTicketQty)) { 
     alert("Quantity must be a number"); 
    } 
} 
document.write("<br>"); 

編輯 - 根據要求。

document.write("<br>"); 
vTicketQty = prompt("Enter No. of Tickets"); 
calcPrice(); 
vTicketQty = parseInt(vTicketQty); 
if (isNaN(vTicketQty)) { 
    vTicketQty = 0; 
} 
document.write("<br>"); 

EDITED - 更像

1功能）

document.write("<br>"); 
calcPrice(); 
vTicketQty = getQty(); 
document.write("<br>"); 

function getQty() { 
    qty = parseInt(prompt("Enter No. of Tickets")); 
    if (isNaN(qty)) { 
     return 0; 
    } 
    return qty; 
} 

2）

document.write("<br>"); 
vTicketQty = prompt("Enter No. of Tickets"); 
calcPrice(); 
vTicketQty = checkNaN(parseInt(vTicketQty)); 
document.write("<br>"); 


function checkNaN(qty) { 
    if (isNaN(qty)) { 
     return 0; 
    } 
    return qty; 
}