title: How to refresh front page after back-end task completed
body: <p>I'm design a web application with python flask, the processing flow is like:</p>
  
  <ol>
  <li>User choose a specified a URL, and ask server site to do some time-consuming task;</li>
  <li>The time-consuming task is then running in a new thread;</li>
  <li>After #2 is done, server will update some info regarding the URL,  I need to refresh the page in #1</li>
  </ol>
  
  <p>I don't know how to notify the "completion" status to front-end so as to refresh the page.</p>
  
  <p>Anyone can help me out?
  Thanks</p>