原生JavaScript实现简易加减乘除计算器

完整代码示例

<!DOCTYPE html>
<html>
 <head>
 <meta charset="UTF-8">
 <title>加减乘除计算器</title> 
 <script type="text/javascript">
 function count(){ 
 var a = parseInt(document.getElementById("txt1").value);
 var b = parseInt(document.getElementById("txt2").value) ;
 var sign = document.getElementById("select").value;
 var result = 0;
  switch(sign){
   case "+": result = a+b;
   break;
   case "-": result = a-b;
   break;
   case "*": result = a*b;
   break;
   case "/": result = a/b;
   break;
   case "%": result = a%b;
   break;
   }
 document.getElementById("answer").value = result;
 }
 </script> 
 </head> 
 <body>
 <input type='text' id='txt1' /> 
 <select id='select'>
  <option value='+'>+</option>
  <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='answer' /> 
 </body>
</html>