JS计算器 - 码农教程

JS处理的一般步骤：

1、先获取元素的对象

2、再通过元素的属性取到相应的值

3、用户输入的数字是字符串，还需要将其转为数值型

 <script type="text/javascript"> 
    function computing(){
      var firstObj = window.document.getElementById("firstNum"); //先获取元素的对象
      var firstVal = parseFloat(firstObj.value);   //再获取元素的值
      var secondObj = window.document.getElementById("secondNum");
      var secondVal = parseFloat(secondObj.value);
      var sign = window.document.getElementById("sign");
      var results = window.document.getElementById("results");
      var res = 0;
     switch(sign.value){ //sign 是对象
         case "+":
            res = firstVal + secondVal;
            break;
        case "-":
            res = firstVal - secondVal;
            break;
        case "*":
             res = firstVal * secondVal;
            break;
        case "/":
             res = firstVal / secondVal;
     }
     results.value =res.toFixed(2);
    }
   </script>
<body>
   firstNum：<input type="text" name="firstNum" value="1" id="firstNum"><br>
   secondNum：<input type="text" name="secondNum" value="2" id="secondNum"><br>
    <select name="signName" id="sign">
        <option value="+">+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
    </select>
    <br>
    <input type="button" value="=" onclick="computing()"><br>
    results：<input type="text" name="results" id="results"><br>
</body>

原文地址：https://www.cnblogs.com/luoxuw/p/11033164.html