纯JavaScript实现简易网页计算器

<!DOCTYPE html>
<html>
 <head>
 <title> new document </title> 
 <script type="text/javascript">
  function count(){
    var txt1  = parseInt( document.getElementById('txt1').value);//获取第一个输入框的值
    var txt2  = parseInt( document.getElementById('txt2').value);//获取第二个输入框的值
    var select = document.getElementById('select').value;//获取选择框的值
    var result = '';
    switch (select)
     {
      case '+':
        result = txt1 + txt2;
        break;
      case '-':
        result = txt1 - txt2;
        break;
      case '*':
        result = txt1 * txt2;
        break;
      case '/':
        result = txt1 / txt2;
        break; 
     }
     document.getElementById('fruit').value = result;//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>