Server.listen() in node gives " Error [ERR_SERVER_ALREADY_LISTEN]: Listen method has been called more than once without closing."

Question

Apologies if some aspects of the question here are unclear as I am new to node & javascript. Please ask for further details

I have a node application that is connected to firebase using socketio. When the application is deployed on heroku, I get the following error:

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; 

The description of the error is on this link :

https://nodejs.org/api/all.html#errors_err_server_already_listen

The listening code on my server.js is as shown:

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

Any idea why this error is occurring? Should I close the server if the listen fails. If yes, how can I do it?

Thank you.

Answer 1

My bad. I got confused as the error was not occurring on my mac. The answer is in the error itself. The error was occurring as the listen method was being called twice. The second call was in some other module.