How To Solve Mongo - couldn't connect to server 127.0.0.1:27017 error?

Problem:

[js] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed: SocketException: Error connecting to 127.0.0.1:27017 :: caused by :: Connection refused :
connect@src/mongo/shell/mongo.js:257:13
@(connect):1:6

Solution
Normally this caused because you didn't start mongod process before you try starting mongo shell.

Start mongod server

 mongod

Open another terminal window and start mongo shell

 mongo