redmine/app/views/attachments/upload.js.erb

var fileSpan = $('#attachments_<%= j params[:attachment_id] %>');
<% if @attachment.new_record? %>
  fileSpan.hide();
  alert("<%= escape_javascript @attachment.errors.full_messages.join(', ') %>");
<% else %>
fileSpan.find('input.token').val('<%= j @attachment.token %>');
fileSpan.find('a.remove-upload')
  .attr({
    "data-remote": true,
    "data-method": 'delete',
    href: '<%= j attachment_path(@attachment, :attachment_id => params[:attachment_id], :format => 'js') %>'
  })
  .off('click');
<% end %>