how to save file upload from the innerHTML javascript?

<script type = "text/javascript">
     var counter = 0;

           function AddFileUpload() {
               var div = document.createElement('DIV');
               div.innerHTML = '<input id="file' + counter + '" name = "file' + counter + '" type="file" /><input id="Button' + counter + '" type="button" value="Remove" onclick = "RemoveFileUpload(this)" />';
               document.getElementById("FileUploadContainer").appendChild(div);
               counter++;
           }
</script>


   <asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent" >

           <span style ="font-family:Arial">Click to add files</span>  

           <br /><br />

           <div id = "FileUploadContainer"  runat="server" >

           </div>
           <br />
           <input id="ButtonAdd" type="button" value="add" onclick = "AddFileUpload()" />
           <asp:Button ID="btnUpload" runat="server" Text="Upload"  />
       <asp:Label ID="lbl2" runat="server" ForeColor="Red"></asp:Label>
           <br />

   </asp:Content>