javascript 计算器

简单计算器

 1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 2 <html xmlns="http://www.w3.org/1999/xhtml">
 3 <head>
 4 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 5 <title>无标题文档</title>
 6 <script type="text/javascript">
 7 window.onload = function(){
 8     var oper = document.getElementById("oper");
 9     var cal = document.getElementById("cal");
10     var result = document.getElementById("result");
11 cal.onclick = function(){
12     var num1 = document.getElementById("num1").value;
13     var num2 = document.getElementById("num2").value;
14     var option = oper.options[oper.selectedIndex].text;
15     switch (option){
16         case "+":
17         result.value =  parseInt(num1) + parseInt(num2);
18         break;
19         case "-":
20         result.value = parseInt(num1) - parseInt(num2);
21         break;
22         case "*":
23         result.value = parseInt(num1) * parseInt(num2);
24         break;
25         case "/":
26         result.value = parseInt(num1) / parseInt(num2);
27         break;
28         }
29 };
30     
31 };
32 
33 </script>
34 </head>
35 <body>
36 <input type="text" id="num1" /><select id="oper">
37 <option>+</option>
38 <option>-</option>
39 <option>*</option>
40 <option>/</option>
41 </select>
42 <input type="text" id="num2" /> = <input type="text" id="result" />
43 <input type="button" id="cal" value="计算" />
44 </body>
45 </html>

总结：

 window.onload = function() 默认函数

 document.getElementById("id")通过id获值

 var option = oper.options[oper.selectedIndex].text; 获得下拉框的选项！这个比较重要