<html>
<head>
<title>checkbox全选全不选</title>
<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>
</head>
 <body>
<p><input type="checkbox" name="all" οnclick="check_all(this,'c')" />全选/全不选</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>
</html>