js-类似邮箱中的删除文件-全选、不选、反选

html代码：

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <title>Title</title>
 6 
 7     <style></style>
 8 
 9     <script>
10         window.onload = function () {
11             var p1 = document.getElementById('id1');
12             var p2 = document.getElementById('id2');
13             var p3 = document.getElementById('id3');
14 
15             var q = document.getElementById('div1');
16             var w = q.getElementsByTagName('input');
17 
18             p1.onclick = function () {
19                 for (var i = 0; i < w.length; i++)
20                     w[i].checked = true;//复选框会变成选中状态
21             };
22 
23             p2.onclick = function () {
24                 for (var i = 0; i < w.length; i++)
25                     w[i].checked = false;
26             }
27 
28             p3.onclick = function () {
29                 for (var i = 0; i < w.length; i++) {
30                     if (w[i].checked == true)
31                         w[i].checked = false;
32                     else
33                         w[i].checked = true;
34                 }
35             }
36 
37         };
38     </script>
39 
40 </head>
41 
42 <body>
43 <input id="id1" type="button" value="全选"/><br>
44 <input id="id2" type="button" value="不选"/><br>
45 <input id="id3" type="button" value="反选"/><br>
46 <div id="div1">
47     <input type="checkbox"/><br>
48     <input type="checkbox"/><br>
49     <input type="checkbox"/><br>
50     <input type="checkbox"/><br>
51     <input type="checkbox"/><br>
52     <input type="checkbox"/><br>
53 </div>
54 </body>
55 
56 </html>