全選/不全選checkbox

<SCRIPT language=javascript>
function unselectall()
{
    if(document.myform.chkAll.checked){
    document.myform.chkAll.checked = document.myform.chkAll.checked&0;
    }    
}
function CheckAll(form)
{
  for (var i=0;i<form.elements.length;i++)
    {
    var e = form.elements[i];
    if (e.Name != "chkAll")
       e.checked = form.chkAll.checked;
    }
}

</script>

<form action="" name="myform">
<input name="FileName" type="checkbox" onclick="unselectall()"><br>
<input name="FileName" type="checkbox" onclick="unselectall()"><br>
<input name="FileName" type="checkbox" onclick="unselectall()"><br>
<input name="FileName" type="checkbox" onclick="unselectall()"><br>
<input name="FileName" type="checkbox" onclick="unselectall()"><br>
<input name="FileName" type="checkbox" onclick="unselectall()"><br><hr>
<input name="chkAll" type="checkbox" id="chkAll" onclick=CheckAll(this.form) value="checkbox">
</form>