Question

我盯着学习Javascript，我试图创建一个计算器，只是乘以2个数字，我在浏览器控制台中收到此错误。有人可以帮忙吗？

   <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Calc</title>
    <style>#result{position: relative; top: 5px;}</style>
</head>
<body>
    <input type="number" id="first"> *
    <input type="number" id="second">
    <br>
    <input type="submit" id="result" value="Check out" onclick="res()"></input> <span id="span"></span> 
    <script>
        function res() {
            var a = document.getElementById("first").value;
            var b = document.getElementById("second").value;
            var span = document.getElementById("span");
            if(a != 0 && b !=0) {
                span.innerHTML = a * b;
            }
            if(a = 0 ||  b = 0) {
                span.innerHTML = "0"; // I know browser can do it automatically without 21 and 22 strings but i need that it works this way.  
            }
        }
    </script>
</body>
</html>

Answer 1

首先，如果您要使用文本输入进行任何数学运算，则必须将它们转换为数字。您可以使用parseInt(num, 10)或parseFloat(num)。

其次，在您的一个if语句中，您实际上并未比较变量a和b，而是为它们分配0。使用两个等号==来比较变量。

第三，您可以使用isNaN(num)检查它们是否为数字。这样做会消除第一个if语句。

＆＃13;

function res() {
  var a = parseFloat(document.getElementById("first").value);
  var b = parseFloat(document.getElementById("second").value);
  var span = document.getElementById("span");
  
  if (isNaN(a) || isNaN(b)) {
    span.innerHTML = "0";
  }
  else {
    span.innerHTML = a * b;
  }
}

＆＃13;

<input type="number" id="first">*
<input type="number" id="second">
<br>
<input type="submit" id="result" value="Check out" onclick="res()"></input> <span id="span"></span>

＆＃13;

Answer 2

在此处查看您的更正代码

<html>
<head>

    <title>Calc</title>
    <style>#result{position: relative; top: 5px;}</style>
</head>
<body>
    <input type="number" id="first"> *
    <input type="number" id="second">
    <br>
    <input type="submit" id="result" value="Check out" onclick="res()"></input> <span id="span"></span> 
    <script>
        function res() {
            var a = document.getElementById("first").value;
            var b = document.getElementById("second").value;
            var span = document.getElementById("span");
            if(a != 0 && b !=0) {
                span.innerHTML = a * b;
            }
            if(a == 0 ||  b == 0) {
                span.innerHTML = "0"; // I know browser can do it automatically without 21 and 22 strings but i need that it works this way.  
            }
        }
    </script>
</body>
</html>

未捕获的ReferenceError：赋值中的左侧无效

2 个答案: