Check/uncheck CheckBox in a GridView using Javascript

 Gridview:

    <asp:GridView runat="server" ID="GV1">

        <Columns>

            <asp:TemplateField>

                <HeaderTemplate>                  

                    <asp:CheckBox ID="chkheader" runat="server" onclick="CheckAll(this)" />

                </HeaderTemplate>

                <ItemTemplate>

                    <asp:CheckBox ID="chkitem" runat="server" />

                </ItemTemplate>

            </asp:TemplateField>

        </Columns>

    </asp:GridView>

   

Javascript

<script type="text/javascript">

        function SelectAll(status) {

            var gv = document.getElementById("<%=GV1.ClientID %>");

            var inputs = gv.getElementsByTagName("input");

            for (var i = 0; i < inputs.length; i++) {

                if (inputs[i].type == 'checkbox') {

                    inputs[i].checked = status;

                }

            }

        }

        function CheckAll(chkheader) {

            if (chkheader.checked) {

                SelectAll(true);

            }

            else {

                SelectAll(false);

            }

        }

    </script>

Note: OnClientClick is not available for checkbox. You can use onclick Event.