If you start up your node project (given that it uses mongo to connect to some database) without starting up your mongo db, you’ll get errors.

For example:
Rickys-MacBook-Pro:TODO_url_authentication rickytsao$ gulp
[22:02:09] Using gulpfile ~/Desktop/TODO_url_authentication/gulpfile.js
[22:02:09] Starting ‘default’…
[22:02:09] Finished ‘default’ after 2.12 ms
[22:02:09] [nodemon] v1.3.7
[22:02:09] [nodemon] to restart at any time, enter rs
[22:02:09] [nodemon] watching: *.*
[22:02:09] [nodemon] starting node server.js
Magic happens at http://localhost:8080
connection error: { [MongoError: connect ECONNREFUSED] name: ‘MongoError’, message: ‘connect ECONNREFUSED’ }

Simply open up another terminal and type in:
mongod
Then the database will start up and you’ll see whole bunch of logs…

2015-07-05T22:05:14.166+0800 W – [initandlisten] Detected unclean shutdown – /data/db/mongod.lock is not empty.
2015-07-05T22:05:14.182+0800 I JOURNAL [initandlisten] journal dir=/data/db/journal
2015-07-05T22:05:14.182+0800 I JOURNAL [initandlisten] recover begin
2015-07-05T22:05:14.187+0800 I JOURNAL [initandlisten] recover lsn: 29046914
2015-07-05T22:05:14.187+0800 I JOURNAL [initandlisten] recover /data/db/journal/j._0
2015-07-05T22:05:14.188+0800 I JOURNAL [initandlisten] recover skipping application of section seq:0 < lsn:29046914 2015-07-05T22:05:14.189+0800 I JOURNAL [initandlisten] recover skipping application of section seq:15301820 < lsn:29046914 2015-07-05T22:05:14.224+0800 I JOURNAL [initandlisten] recover cleaning up 2015-07-05T22:05:14.224+0800 I JOURNAL [initandlisten] removeJournalFiles 2015-07-05T22:05:14.252+0800 I JOURNAL [initandlisten] recover done 2015-07-05T22:05:14.297+0800 I JOURNAL [durability] Durability thread st