title: Notification server to client, post a res.render(), after a time-intensive function has ended
body: <p>When a user follows a route in my application, a time consuming function begins executing.</p>
  
  <p>Can i render a page on that route in the beginning of the request, then when the time-intensive function ends, send something to that page, a message, to notify the user that the time-intensive work is done?</p>
  
  <p>And then, when the page that the user is on, receives the message, it displays a hidden div with a link?</p>
  
  <p>Are Flash messages able to do that?</p>