jQuery upload to Sinatra

upload.rb

require 'slim'
require 'sinatra'

template :upload do 
  <<-END
    head 
      script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"
      javascript:
        $(document).ready(function() {
          $('#upload :button').click(function(){
            $.ajax({
            url: '/',
            type: 'POST',
            success: function(response) { alert("Success! " + response) },
            error: function(response) { alert("Nope. " + response.responseText) },
            data: new FormData($('#upload')[0]),
            cache: false,
            contentType: false,
            processData: false
          });
        });
      });
    body
      form id='upload' enctype='multipart/form-data'
        input type='file' name='filename'
        input type='button' value='Upload'
  END
end

get '/' do 
  slim :upload
end

post '/' do 
  [
    [200, "You uploaded #{params['filename'][:tempfile].size} bytes!"],
    [400, "You do not smell good enough to upload to this site! Shower and try again."],
    [400, "I can tell you've been dabbling in Python. No uploads until you've repented."],
    [400, "I can smell the fear on you. Cowards cannot upload to this site!"]
  ].sample
end