Having examples right away:
http://www.wowbox.com.tw/blog/article.asp?id=2923
<script type="text/javascript">
function check_all(obj,cName)
{
var checkboxs = document.getElementsByName(cName);
for(var i=0;i<checkboxs.length;i++){checkboxs[i].checked = obj.checked;}
}
</script>
<body>
<p><input type="checkbox" name="all" onclick="check_all(this,'c')" />全選/全不選</p>
<p><input type="checkbox" name="c" value="" /></p>
<p><input type="checkbox" name="c" value="" /></p>
<p><input type="checkbox" name="c" value="" /></p>
<p><input type="checkbox" name="c" value="" /></p>
</body>
