code: function ping() {
          var value = +new Date();
  
          primus.timers.clear('ping');
          primus._write('primus::ping::'+ value);
          primus.emit('outgoing::ping', value);
          primus.timers.setTimeout('pong', pong, primus.options.pong);
        }
docs: We should send a ping message to the server.
  
  @api private