js实现checkbox的全选和全不选功能

<form name="form1" method="post" action="manage.php?act=sub">
    <input type="checkbox" name="mm[]" value="<?=$row['0']?>" onClick="checkAll(this, 'mm')">
    <!--checkbox 实现选择多条记录-->
    <input type="submit" name="Submit" value="删除" onClick="return(confirm('确认要删除吗？'))">
</form>
<input type="checkbox" name='mm' onClick="checkItem(this, 'mm[]')"></br>
<input type="checkbox" name='mm' onClick="checkItem(this, 'mm[]')"></br>
<input type="checkbox" name='mm' onClick="checkItem(this, 'mm[]')"></br>
<input type="checkbox" name='mm' onClick="checkItem(this, 'mm[]')">
<!-- JS实现全选/不全选的代码 -->
<script language=Javascript>
function checkAll(e, itemName)
{
    var aa = document.getElementsByName(itemName);
    for (var i=0; i<aa.length; i++)
        aa[i].checked = e.checked;
}
function checkItem(e, allName)
{
    var all = document.getElementsByName(allName)[0];
    if(!e.checked) all.checked = false;
    else
    {
        var aa = document.getElementsByName(e.name);
        for (var i=0; i<aa.length; i++)
            if(!aa[i].checked) return;
        all.checked = true;
    }
}
</script>

    $num=$_POST['mm'];//这里得到一个POST数组；
    $str=implode(',', $num); //把数组值分开；
    $query="delete from `ad` where `id` IN({$str});"; //SQL语法，IN条件语句