JavaScript统计表单中Checkbox选中数量的实现方法

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>检测表单多选框的选择个数</title>
<meta http-equiv="content-type" content="text/html;charset=gb2312">
</head>
<body>
<script language="javascript">
<!--
function anyCheck(form) {
var total = 0;
var max = form.ckbox.length;
for (var idx = 0; idx < max; idx++) {
if (eval("document.playlist.ckbox[" + idx + "].checked") == true) {
  total += 1;
  }
}
alert("您选择了 " + total + " 个选项！");
}
//-->
</script>
<form method="post" name="playlist">
1<input type="checkbox" name="ckbox" value="1">
2<input type="checkbox" name="ckbox" value="2">
3<input type="checkbox" name="ckbox" value="3">
4<input type="checkbox" name="ckbox" value="4">
5<input type="checkbox" name="ckbox" value="5">
6<input type="checkbox" name="ckbox" value="6">
<br><input type="button" value="检测选择个数" onClick="anyCheck(this.form)">
</form>
</body>
</html>