index.html

<p>Hello

<script>
var xhr = new XMLHttpRequest();
xhr.open('GET', '/stream');
xhr.seenBytes = 0;

xhr.onreadystatechange = function() {
  console.log("state change.. state: "+ xhr.readyState);

  if(xhr.readyState == 3) {
    var newData = xhr.response.substr(xhr.seenBytes);
    console.log("newData: <<" +newData+ ">>");
    document.body.innerHTML += "New data: <<" +newData+ ">><br />";

    xhr.seenBytes = xhr.responseText.length;
    console.log("seenBytes: " +xhr.seenBytes);
  }
};

xhr.addEventListener("error", function(e) {
  console.log("error: " +e);
});

console.log(xhr);
xhr.send();
</script>

server.rb

require 'goliath'

class Server < Goliath::API

  def response(env)
    case env['REQUEST_PATH']
    when /index/ then
      [200, {}, IO.read('index.html')]

    when /stream/ then
      EM.add_periodic_timer(3) do
        env.stream_send("data event! ... ")
      end

      headers = {'Content-Type' => 'application/x-javascript'}
      [200, headers, Goliath::Response::STREAMING]
    end
  end
end