JS最基础的获取元素的值实现加减乘除运算

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>事件</title>
<link href="css.css" rel="stylesheet" type="text/css"/>
</head>

<body>
  <div >
   <!DOCTYPE  HTML>
<html >
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>数组</title>
<script type="text/javascript">
   function count(){
       
    //获取第一个输入框的值
    var num1 = parseInt(document.getElementById("txt1").value);
    var num2 = parseInt(document.getElementById("txt2").value);
    var fu =document.getElementById("select").value;
    var jisuan;
    switch(fu)
    {
        case "+":jisuan= num1+num2;break;
        case "-":jisuan= num1-num2;break;
        case "*":jisuan= num1*num2;break;
        case "/":jisuan= num1/num2;break;
        default:break;
        }
    
    document.getElementById("fruit").value = jisuan;
    //获取第二个输入框的值
    //获取选择框的值
    //获取通过下拉框来选择的值来改变加减乘除的运算法则
    //设置结果输入框的值 
    
   }
  </script> 
</head>
<body>
<input type='text' id='txt1' /> 
   <select id='select'>
        <option value='+'>+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
   </select>
   <input type='text' id='txt2' /> 
   <input type='button' value=' = ' onClick="count()" /> <!--通过 = 按钮来调用创建的函数,得到结果--> 
   <input type='text' id='fruit' />   
</body>
</html>
  </div>

</body>
</html>
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