javascript - 需要使用带有 try、catch 和 throw 异常的 javascript。我想用它来检查文本框以确保它是数字而不是字母

Question

当我添加测试功能时，它不起作用。但是，当我取出测试函数时，它可以工作，但仍然将任何无数字显示为 nan。

HTML 代码:

        <h2>How many male books would you like to order? : <input type="text" id ="maleTotal"/>
        <input type="button" onClick="maleBook()" Value = "Total" />
        <p> The total is: <br>
        <span id = "result"></span></h2>

      </form>

Javascript代码:

function maleBook(){
    var malePrice = 14.95;
    var tax = .06875;
    maleTotal = document.getElementById("maleTotal").value;
    totalTax = tax * malePrice * maleTotal
    document.getElementById("result").innerHTML = maleTotal * malePrice + totalTax;
}

function test() {
  var x;
  x = document.getElementById("maleTotal").value;
  try { 
    if(x == "") window.alert "empty";
    if(isNaN(x)) window.alert"not a number";
      }
  catch(err) {
    message.innerHTML = "Input is " + err;
  }

Answer 1

一方面，您在警报中缺少括号。它应该是这样的: window.alert("your message");

另一方面，您在 if 语句中缺少括号{}

最后，您需要调用 test() 函数，也许将其链接在maleBook() 的末尾

function maleBook(){
    var malePrice = 14.95;
    var tax = .06875;
    maleTotal = document.getElementById("maleTotal").value;
    totalTax = tax * malePrice * maleTotal
    document.getElementById("result").innerHTML = maleTotal * malePrice + totalTax;
    test();
}

function test() {
  var x = document.getElementById("maleTotal").value;
  try { 
    if(x == "") { 
        window.alert( "empty");
    }
    if(isNaN(x)) {
        window.alert("not a number");
    }
  }
  catch(err) {
    message.innerHTML = "Input is " + err;
  }
}