src/connect/index.js
function ping (){
    clearTimeout( ping.timer );
    ping.timer = setTimeout(function(){
      b9.send({ type: 'ping', time: Date.now() });
    }, b9._interval );
  }
function ping (){
    clearTimeout( ping.timer );
    ping.timer = setTimeout(function(){
      b9.send({ type: 'ping', time: Date.now() });
    }, b9._interval );
  }
function ping ( ) { clearTimeout ( ping . timer ) ; ping . timer = setTimeout ( function ( ) { b9 . send ( { type : 'ping' , time : Date . now ( ) } ) ; } , b9 . _interval ) ; }
keep the connection alive
@private method
keep the connection alive