Check/Uncheck checkboxes in GridView using JavaScript

<script type="text/javascript">

    function SelectAll(id) {

        var frm = document.forms[0];

        for (i=0;i<frm.elements.length;i++) {

            if (frm.elements[i].type == "checkbox") {

                frm.elements[i].checked = document.getElementById(id).checked;

            }

        }

    } 

</script>

<!-- assuming that SqlDataSource1 is the datasource for my GridView -->

<asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1" Width="400px">

    <Columns>

        <asp:TemplateField>

            <AlternatingItemTemplate>

                <asp:CheckBox ID="CheckBox1" runat="server" />

            </AlternatingItemTemplate>

            <ItemTemplate>

                <asp:CheckBox ID="CheckBox1" runat="server" />

            </ItemTemplate>

            <HeaderTemplate>

                <asp:CheckBox ID="cbSelectAll" runat="server" Text="Select All" />

            </HeaderTemplate>

            <HeaderStyle HorizontalAlign="Left" />

            <ItemStyle HorizontalAlign="Left" />

        </asp:TemplateField>

    </Columns>

</asp:GridView>

Protected Sub GridView1_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GridView1.RowDataBound

    If (e.Row.RowType = DataControlRowType.Header) Then

        'adding an attribute for onclick event on the check box in the header

        'and passing the ClientID of the Select All checkbox

        DirectCast(e.Row.FindControl("cbSelectAll"), CheckBox).Attributes.Add("onclick", "javascript:SelectAll('" & _

            DirectCast(e.Row.FindControl("cbSelectAll"), CheckBox).ClientID & "')")

    End If

End Sub

protected void GridView1_RowDataBound(object sender, System.Web.UI.WebControls.GridViewRowEventArgs e) {

    if (e.Row.RowType == DataControlRowType.Header) {

        //adding an attribute for onclick event on the check box in the header

        //and passing the ClientID of the Select All checkbox

        ((CheckBox)e.Row.FindControl("cbSelectAll")).Attributes.Add("onclick", "javascript:SelectAll('" + ((CheckBox)e.Row.FindControl("cbSelectAll")).ClientID + "')");

    }

}

<script type="text/javascript">

    // Let's use a lowercase function name to keep with JavaScript conventions

    function selectAll(invoker) {

        // Since ASP.NET checkboxes are really HTML input elements

        //  let's get all the inputs

        var inputElements = document.getElementsByTagName('input');

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

            var myElement = inputElements[i];

            // Filter through the input types looking for checkboxes

            if (myElement.type === "checkbox") {

               // Use the invoker (our calling element) as the reference 

               //  for our checkbox status

                myElement.checked = invoker.checked;

            }

        }

    } 

</script>

<!-- assuming that SqlDataSource1 is the datasource for my GridView -->

<asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1">

    <Columns>

        <asp:TemplateField>

            <AlternatingItemTemplate>

                <asp:CheckBox ID="CheckBox1" runat="server" />

            </AlternatingItemTemplate>

            <ItemTemplate>

                <asp:CheckBox ID="CheckBox1" runat="server" />

            </ItemTemplate>

            <HeaderTemplate>

                <asp:CheckBox ID="cbSelectAll" runat="server" Text="Select All" OnClick="selectAll(this)" />

            </HeaderTemplate>

            <HeaderStyle HorizontalAlign="Left" />

            <ItemStyle HorizontalAlign="Left" />

        </asp:TemplateField>

    </Columns>

</asp:GridView>