Heroku Node.js app giving errors

I'm trying to deploy my first app to heroku, but something is a miss.

I have gone into the logs and this is what is happening. Anyone have any ideas?

it would be much appreciated or is there any other information I can get that will reveal whats happening? It is working on local host fine, even through heroku's local host at 5000.

port is set like this. var port = process.env.PORT || 3000;

logs below

2017-05-29T16:28:57.730817+00:00 app[web.1]: 

2017-05-29T16:28:57.730818+00:00 app[web.1]: ReferenceError: err is not defined

2017-05-29T16:28:57.730819+00:00 app[web.1]:     at NativeConnection.<anonymous> (/app/app.js:19:17)

2017-05-29T16:28:57.730819+00:00 app[web.1]:     at emitOne (events.js:96:13)

2017-05-29T16:28:57.730820+00:00 app[web.1]:     at NativeConnection.emit (events.js:188:7)

2017-05-29T16:28:57.730821+00:00 app[web.1]:     at Immediate.<anonymous> (/app/node_modules/mongoose/lib/connection.js:322:19)

2017-05-29T16:28:57.730822+00:00 app[web.1]:     at runCallback (timers.js:651:20)

2017-05-29T16:28:57.730822+00:00 app[web.1]:     at tryOnImmediate (timers.js:624:5)

2017-05-29T16:28:57.730823+00:00 app[web.1]:     at processImmediate [as _immediateCallback] (timers.js:596:5)

2017-05-29T16:28:57.828280+00:00 heroku[web.1]: State changed from starting to crashed

Thanks in advance.

via Middi