抱歉，如果这里的问题的某些方面不清楚，因为我是新的节点和JavaScript。详情请咨询
我有一个使用socketio连接到firebase的node应用程序。当应用程序部署在heroku上时，我得到以下错误：

Error [ERR_SERVER_ALREADY_LISTEN]: Listen method has been called more than once without closing. 
Nov 01 19:57:38  app/web.1:     at Server.listen (net.js:1446:11) 
Nov 01 19:57:38  app/web.1:     at exports.default (/app/dist/server.js:8226:11) 
Nov 01 19:57:38  app/web.1:     at Object.<anonymous> (/app/dist/server.js:191:21) 
Nov 01 19:57:38  app/web.1:     at __webpack_require__ (/app/dist/server.js:20:30) 
Nov 01 19:57:38  app/web.1:     at Object.<anonymous> (/app/dist/server.js:47:19) 
Nov 01 19:57:38  app/web.1:     at __webpack_require__ (/app/dist/server.js:20:30) 
Nov 01 19:57:38  app/web.1:     at /app/dist/server.js:40:18 
Nov 01 19:57:38  app/web.1:     at Object.<anonymous> (/app/dist/server.js:43:10) 
Nov 01 19:57:38  app/web.1:     at Module._compile (module.js:641:30) 
Nov 01 19:57:38  app/web.1:     at Object.Module._extensions..js (module.js:652:10) 
Nov 01 19:57:38  app/web.1: /app/dist/server.js:212 
Nov 01 19:57:38  app/web.1:         throw error;

错误的描述在这个链接上：
https://nodejs.org/api/all.html#errors_err_server_already_listen
我的server.js上的监听代码如下所示：

const server = http.createServer(app).listen(port)

知道为什么会出现这个错误吗？如果监听失败，我应该关闭服务器吗？如果是，我该如何做？
谢谢