如何使用isNaN來檢查輸入是否是數字？

我想在我的代碼中限制符號，負數和所有其他非相對的東西。我的教授告訴我使用isNaN，但我不知道如何在我的代碼中應用。有人可以幫我解決這個問題嗎？我重視我的代碼如下
如何使用isNaN來檢查輸入是否是數字？

<!-- Network Latency Calculator --> 

<html> 
<head> 
    <meta charset = "utf-8"> 
    <title>Network Latency Calculation</title> 
    <script> 

    var firstNumber; // first string entered by user 
    var secondNumber; // second string entered by user 
var thirdNumber; // third string entered by user 
var fourthNumber; // fourth string entered by user 
    var number1; // first number to add 
    var number2; // second number to add 
var number3; // third number to add 
var number4; // fourth number to add 
    var sum; // sum of number1 and number2 and number3 and number4 
var sumresult; 




    // read in first number from user as a string 
    firstNumber = window.prompt("Enter the Propagation time (no negative number, letter, blank space, and symbol is not allow)"); 

    // read in second number from user as a string 
    secondNumber = window.prompt("Enter the Transmission time (no negative number, letter, blank space, and symbol is not allow)"); 


// read in third number from user as a string 
    thirdNumber = window.prompt("Enter the Queuing time (no negative number, letter, blank space, and symbol is not allow)"); 


// read in fourth number from user as a string 
    fourthNumber = window.prompt("Enter the Propagation delay (no negative number, letter, blank space, and symbol is not allow)"); 








    // convert numbers from strings to integers 
    number1 = parseFloat(firstNumber); 
    number2 = parseFloat(secondNumber); 
number3 = parseFloat(thirdNumber); 
number4 = parseFloat(fourthNumber); 

    sum = number1 + number2 + number3 + number4; // add the numbers 

sumresult = parseFloat(sum); 


    // display the results 
    document.writeln("<h1>The network latency is " + sum + "</h1>"); 
document.writeln("<p>Propagation time " + number1 + "</p>"); 
document.writeln("<p>Transmission time " + number2 + "</p>"); 
document.writeln("<p>Queuing time " + number3 + "</p>"); 
document.writeln("<p>Propagation delay " + number4 + "</p>"); 

if (sumresult < 1) 
     document.writeln("<p>Network performance is good.</p>"); 
else (document.writeln("<p>Warning: Network performance needs improvement.</p>")); 






    </script> 
</head><body></body>

來源

2017-04-27 Jay Huang

'isNaN（其他）'爲真，如果'whatever'不一個數字 - 注意：即使'1.23「是一個字符串，isNaN（」1.23「）將是假的 - 所以如果你想像這樣使用它們，你仍然需要將值解析/強制爲'Number' –

在生產Web應用程序，你就不會提示輸入數字用戶 - 你會顯示一個表單供用戶填寫。

但是，因爲我們正在與玩具應用程序時，你可以簡單地重複提示，直到用戶得到它的權利：

function getNumberFromUser(promptText) { 
    var n = NaN; 
    while(isNaN(n) || (n < 0)) { 
     var nString = window.prompt(promptText); 
     n = parseFloat(nString); 
    } 
    return n; 
} 
var number1 = getNumberFromUser("Enter the Propagation time (no negative number, letter, blank space, and symbol is not allow)"); 
var number2 = getNumberFromUser("Enter the Transmission time (no negative number, letter, blank space, and symbol is not allow)"); 
//etc

來源

2017-04-27 00:35:18

我還沒有測試過這個，但是如果他們輸入任何正數，那麼是不是你的while語句要重複？ – jas7457

@ jas7457 - Doh！它應該是'<', not '> ='。我會解決它。 –

我應該在promt之前添加代碼嗎？因爲webstie不運行。 –

如何使用isNaN來檢查輸入是否是數字？

回答

相關問題