check uncheck checkbox in a gridview using javascript

<script type="text/javascript">

 function SelectAllCheckboxes(cbSelectAll)

 {

var gvcheck = document.getElementById('gvuseredit');

var i;

if (cbSelectAll.checked)

{

for (i = 0; i < gvcheck.rows.length-1; i++)

{

var inputs = gvcheck.rows[i].getElementsByTagName('input');

inputs[0].checked = true;

}

      }

      else

      {

            for (i = 0; i < gvcheck.rows.length-1; i++)

{

var inputs = gvcheck.rows[i].getElementsByTagName('input');

inputs[0].checked = false;

}

      }

}

function Selectchildcheckboxes(header)

{

var ck = header;

var count = 0;

var gvcheck = document.getElementById('gvuseredit');

var headerchk = document.getElementById(header);

var rowcount = gvcheck.rows.length;

for (i = 1; i < gvcheck.rows.length-1; i++)

{

var inputs = gvcheck.rows[i].getElementsByTagName('input');

if (inputs[0].checked)

 {

  count++;

       }

       }

if (count == rowcount-1)

{

 cbSelectAll.checked = true;

}

else

{

 cbSelectAll.checked = false;

}

}

script>

<asp:GridView ID="gvuseredit" runat="server" AllowSorting="true" AutoGenerateColumns="false"

AllowPaging="true" ShowFooter="true"

onrowdatabound="gvuseredit_RowDataBound">

<Columns>

<asp:TemplateField HeaderText="Select User">

<HeaderTemplate>

<asp:CheckBox ID="cbSelectAll" runat="server" onclick="javascript:SelectAllCheckboxes(this)" Text="Select All" />

HeaderTemplate>

<ItemTemplate>

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

ItemTemplate>

<FooterTemplate>

<asp:Button ID="btndeleteUser" runat="server" Text="Delete" />

FooterTemplate>

<HeaderStyle Width="" />

asp:TemplateField>

<asp:TemplateField HeaderText="Edit" ShowHeader="False" HeaderStyle-HorizontalAlign="Left">

<EditItemTemplate>

<asp:LinkButton ID="lbkUpdate" runat="server" CausesValidation="True" CommandName="Update"

Text="Update">asp:LinkButton>

<asp:LinkButton ID="lnkCancel" runat="server" CausesValidation="False" CommandName="Cancel"

Text="Cancel">asp:LinkButton>

EditItemTemplate>

<ItemTemplate>

<asp:LinkButton ID="lnkEdit" runat="server" CausesValidation="False" CommandName="Edit"

Text="Edit">asp:LinkButton>

ItemTemplate>

<HeaderStyle Width="100px" />

<ItemStyle Width="100px" />

asp:TemplateField>

<asp:TemplateField HeaderText="rec ID">

<ItemTemplate>

<asp:Label ID="lblrecID" runat="server" Text='<%# Bind("recID") %>'>asp:Label>

ItemTemplate>

<EditItemTemplate>

<asp:Label ID="txtrecID" runat="server" Text='<%# Bind("recID") %>'>asp:Label>

EditItemTemplate>

<HeaderStyle Width="" />

asp:TemplateField>

<asp:TemplateField HeaderText="User Name">

<ItemTemplate>

<asp:Label ID="lblUserName" runat="server" Text='<%# Bind("UserName") %>'>asp:Label>

ItemTemplate>

<EditItemTemplate>

<asp:Label ID="lblUserName" runat="server" Text='<%# Bind("UserName") %>'>asp:Label>

EditItemTemplate>

<HeaderStyle Width="100px" />

<ItemStyle Width="100px" />

asp:TemplateField>

<asp:TemplateField HeaderText="Password">

<ItemTemplate>

<asp:Label ID="lblpwd" runat="server" Text='<%# Bind("pwd") %>'>asp:Label>

ItemTemplate>

<EditItemTemplate>

<asp:Label ID="lbpwd" runat="server" Text='<%# Bind("pwd") %>'>asp:Label>

EditItemTemplate>

<HeaderStyle Width="100px" />

<ItemStyle Width="100px" />

asp:TemplateField>

Columns>

asp:GridView>

protected void gvuseredit_RowDataBound(object sender, GridViewRowEventArgs e)

{

if (e.Row.RowType == DataControlRowType.DataRow)

{

CheckBox headerchk =    (CheckBox)gvuseredit.HeaderRow.FindControl("cbSelectAll");

CheckBox childchk = (CheckBox)e.Row.FindControl("chkbdeleteuser");

childchk.Attributes.Add("onclick", "javascript:Selectchildcheckboxes('" + ((System.Web.UI.Control)(headerchk)).ClientID + "')");

}

}