In version 6.4.1, in the 'onPacket' method of 'engine.io/build/socket.js', the 'pong' event does not execute 'this.pingIntervalTimer.refresh()', while in the latest version 6.5.1, it does execute. The 'refresh' method was introduced in Node.js v10.2, so it throws an exception when executed in lower versions, resulting in 'this.pingIntervalTimer.refresh() is not a function' error and causing the service to crash. Please document this situation to prevent errors for users using lower versions of Node.js.