判断checkbox选择的个数 多浏览器_javascript技巧

就是不能让用户选择超过5个checkbox

<title> New Document </title> <meta name="Generator" content="EditPlus"> <meta name="Author" content=""> <meta name="Keywords" content=""> <meta name="Description" content=""> <script language="JavaScript"> <!-- var ii = 0; function boxnum(){ var box = document.getElementsByName("c"); for(var i=0;i<box.length;i++){ box[i].onclick = function chk(){ if(this.checked && ii <= 5) ii += 1; if(! this.checked) ii -= 1; if(ii>5){ ii -=1; this.checked = false;alert('最多不能超多5个主营项目！请重新选择！');} } } } window.onload = boxnum; //--> </script> <table cellspacing="0" border="1" width="200"> <tr> <td><input type="checkbox" name="c"></td> <td><input type="checkbox" name="c"></td> <td><input type="checkbox" name="c"></td> </tr> <tr> <td><input type="checkbox" name="c"></td> <td><input type="checkbox" name="c"></td> <td><input type="checkbox" name="c"></td> </tr> <br><input onclick="runEx('runcode24277')" type="button" value="运行代码"> <input onclick="doCopy('runcode24277')" type="button" value="复制代码"> <input onclick="doSave(runcode24277)" type="button" value="保存代码">[Ctrl+A 全选 注:<a href="http://www.jb51.net/article/23421.htm" title="查看具体详情" target="_blank">如需引入外部Js需刷新才能执行</a>]<br><strong>第二种方法<br></strong><div class="htmlarea"><textarea id="runcode15991"> <meta http-equiv="Content-Type" content="text/html; charset=gb2312"> <title></title>