Check and Uncheck all Checkboxlist using javascript in asp.net

///HTML

<asp:CheckBoxList ID="CheckBoxList1" RepeatDirection="Vertical" runat="server" onclick="javascript: changeSelectAll ()">
                    </asp:CheckBoxList>

<asp:CheckBox ID="CheckBox1" runat="server" onclick="javascript: CheckBoxListSelect (this.id)" />  


//CheckBoxList function

function CheckBoxListSelect(chkid, chblid) {
       var chkBoxList = document.getElementById('<%= CheckBoxList1.ClientID %>');
       var chkB = document.getElementById(chkid);
       if (chkB.checked) {
           var chkBoxCount = chkBoxList.getElementsByTagName("input");
           for (var i = 0; i < chkBoxCount.length; i++) {
               chkBoxCount[i].checked = true;
           }
       }
       if (!chkB.checked) {
           var chkBoxCount = chkBoxList.getElementsByTagName("input");
           for (var i = 0; i < chkBoxCount.length; i++) {
               chkBoxCount[i].checked = false;
           }
       }

       return false;
   }


//CheckBoxList function


   function changeSelectAll() {
       var chkBoxList = document.getElementById('<%= CheckBoxList1.ClientID %>');
       var chkb = document.getElementById('<%= CheckBox1.ClientID %>')
       var chekb = true;
       var chkBoxCount = chkBoxList.getElementsByTagName("input");
       for (var i = 0; i < chkBoxCount.length; i++) {
           if (!chkBoxCount[i].checked) {
               chekb = false;
               break;
           }
       }
       if (chekb) { chkb.checked = true; } else { chkb.checked = false; }
       return false;
   }