title: How to send notification from website when client's browser is closed?
body: <p>I created a messenger (on web) and i want this website send people notification when someone send them a message (and receiver's browser is close).
  I seen before in few website they can do that.
  Thank you.
  i mean First (when user come to my website), site show something like javascript <code>alert();</code> with (almost) this text :
  This website want send you notification</p>
  <p>and two buttons: allow , deny</p>