title: How to send message from server to client in web application
body: <p>Recently, I came across this kind of need. The client(web browser) requests for a task to be done asynchronously at the server side, then the client leaves it behind.</p>
  
  <p>When the server finishes the task, it will notify the client by sending some message.</p>
  
  <p>So, my question is:</p>
  
  <p>Is there a way to send message(plain text, json, etc) from the server side to the client initiatively?</p>