title: Socket.io Check connection
body: <p>I want to check if the client is connected to socket server.
  I don't mean the disconnect event.
  Just wanted to check if it is connected to socket server on the client side.</p>
  <p>When it is disconnected, I can find bellow image.
  <a href="https://i.stack.imgur.com/If6rH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/If6rH.png" alt="enter image description here" /></a></p>
  <p>I think this means it check connection with specific time interval.
  I can't find this function.
  How can I check connection?</p>