Register your js file and call js function Code behind site in .net

  ScriptManager.RegisterStartupScript(this, GetType(), "a_key", "<script type='text/javascript' src='test.js'></script> <script type='text/javascript'>kk();</script> ", 

Upload File Validate Type and Size in .net

<script type="text/javascript">
 
    function checkfilesize(source, arg) {
        var flag1 = true;
        tt = "";

        var totalsize = 0;
   
        if (document.getElementById('<%= FileUploadidfcfile.ClientID %>').value != "" && flag1 == true) {
            var fSize = (document.getElementById('<%= FileUploadidfcfile.ClientID %>').files[0].size / 1024);
            totalsize = parseInt(fSize);
            var actualSize = fSize;
            fSize = (Math.round((fSize / 1024) * 100) / 100)
            if (parseInt(fSize) > 10) {
                arg.IsValid = false;
            } else
            {
                arg.IsValid = true;

            }
        }
     

    }
</script>
 <asp:FileUpload ID="FileUploadidfcfile" runat="server" />
  <asp:RequiredFieldValidator ID="RequiredFieldValidator2" ControlToValidate="FileUploadidfcfile"
                    Display="Dynamic" runat="server" ErrorMessage="please select  file" ForeColor="Red"
                    ValidationGroup="submit"></asp:RequiredFieldValidator>
                     <asp:CustomValidator ID="NewPasswordCustomValidator" runat="server" Display="Dynamic"
                                                                    ErrorMessage="Max file size 10mb"  ForeColor="Red" ControlToValidate="FileUploadidfcfile" ClientValidationFunction="checkfilesize"
                                                                    OnServerValidate="extentionvalidation_ServerValidate" ValidationGroup="submit"
                                                                    EnableClientScript="true"></asp:CustomValidator>
                  <asp:RegularExpressionValidator ID="RegularExpressionValidatorfile2" CssClass="errorMsg"
                                                                    runat="server" ErrorMessage="Please select correct file(pdf,sip,xls,xlsx)" ForeColor="Red" ValidationExpression="^.*\.(XLS|xls|XLSX|xlsx|pdf|PDF|ZIP|zip)$"
                                                                    ControlToValidate="FileUploadidfcfile" ValidationGroup="submit" Display="Dynamic"> </asp:RegularExpressionValidator>
   






  protected void extentionvalidation_ServerValidate(object sender, ServerValidateEventArgs args)
    {
        args.IsValid = false;
        if (FileUploadidfcfile.FileBytes.Length  > 10491876)
        {
            args.IsValid = false;
       
        }
    }

Find Control UserControl to UserControl , Find Control of Master page, Find html Control of Master page,Find Control in parent page

UserControl objOfUserControl = (UserControl)Page.FindControl("UserControlID");
        TextBox txtLocation = objOfUserControl.FindControl("txtLocation") as TextBox;
        txtLocation.Enabled = false;

 ContentPlaceHolder MainContent = Page.Master.FindControl("ContentPlaceHolder2") as ContentPlaceHolder;
        HtmlGenericControl divviewgride = (HtmlGenericControl)MainContent.FindControl("divviewgride") as HtmlGenericControl;
        divviewgride.Visible = true;

 ContentPlaceHolder MainContent = Page.Master.FindControl("ContentPlaceHolder2") as ContentPlaceHolder;
        LinkButton ResultsLabel = MainContent.FindControl("lnkTags") as LinkButton;
        ResultsLabel.Visible = false;

SubString in sql for File Extension

SELECT RIGHT('myFile3333333333333333.txt',
               CHARINDEX('.', REVERSE('myFile.txt'))-1) AS 'File Extension'


case lower(RIGHT(dc.UploadFile,
               CHARINDEX('.', REVERSE('.zip'))-1)) when 'xls' then 'ver11xls_icon'  when 'zip' then 'ver11zip_icon' else 'none' end