How do I add more files to a multiple upload with out clearing the current files

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VB

ASP.NET

Javascript

I have the code to do a multiple upload, but I can not find any example where it shows me how to add multiple files and then before upload add more files. It clears out the current files in the file upload every time I click it and does not keep the files.

I know that this is how it is supposed to work but is there any work around ?

What I have tried:

I have not tried anything since I can't find any examples

My tag for the multiple file upload

<asp:FileUpload ID="FileUpload1"  AllowMultiple="true" runat="server" Font-Names="Verdana" Visible="True" Width="265px" Font-Size="X-Small" Height="23px" onchange="javascript:updateList()" />

My code to load the files in a list

<pre> updateList = function () {
var input = document.getElementById('ctl00_ContentPlaceHolder1_FileUpload1');
var output = document.getElementById('fileList');
var FileList = document.getElementById('SelectedFilesHeader');

FileList.style.display = "Block";
output.innerHTML = '<ul ID="ctl00_ContentPlaceHolder1_ulInputFiles">';
 for (var i = 0; i < input.files.length; ++i) {
      output.innerHTML += '<li ID="liInputFiles_' + i +'">' + input.files.item(i).name + '<input type="button" Value="X" ID="btnInputFiles_' + i +'" /></li > ';
}
output.innerHTML += '</ul>'; }