js gridview中checkbox的全选与全不选

1.html：

   <asp:GridView runat="server" ID="gvAddBySR" AutoGenerateColumns="False" HorizontalAlign="Left"
             Width="100%" EmptyDataText="<%$ Resources:GlobalResource,  NoData%>">
             <Columns>
                 <asp:TemplateField HeaderStyle-Width="7%">
                     <HeaderTemplate>
                         <input id="CheckAll" type="checkbox" onclick="selectAll(this);" />
                     </HeaderTemplate>
                     <ItemTemplate>
                         <asp:CheckBox runat="server" ID="ck" class="ck" onclick="getCk(this);"/>
                     </ItemTemplate>
                 </asp:TemplateField>

2.js

  function selectAll(obj) {
          var idAll = obj;
          Ced = idAll.checked;
          UCed = idAll.form.elements;
          var c = UCed.length;
          for (i = 0; i < UCed.length; i++) {
              if (UCed[i].type == "checkbox" && UCed[i] != idAll.id) {
                  if (UCed[i].checked != Ced) {
                      UCed[i].click();
                  }
              }
          }
      }