Mern throws error, crashes, immediately after starting server

mern start, then:

> mern-starter@1.0.0 start /Users/me/MernTest
> cross-env NODE_ENV=development node index.js

MERN is running on port: 8000! Build something amazing!

/Users/me/MernTest/node_modules/mongodb/lib/server.js:236
        process.nextTick(function() { throw err; })
                                      ^
Error: connect ECONNREFUSED 127.0.0.1:27017
    at Object.exports._errnoException (util.js:870:11)
    at exports._exceptionWithHostPort (util.js:893:20)
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1062:14)

npm ERR! Darwin 15.3.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "start"
npm ERR! node v4.3.1
npm ERR! nom  v3.7.2
npm ERR! code ELIFECYCLE
npm ERR! mern-starter@1.0.0 start: `cross-env NODE_ENV=development node index.js`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the mern-starter@1.0.0 start script 'cross-env NODE_ENV=development node index.js'.

[ghoshnirmalya]

First, you will have to install and run mongoDB. Follow the following steps:

1. brew update
2. brew install mongodb
3. brew install mongodb --with-openssl
4. brew install mongodb --devel
5. sudo mkdir -p /data/db
6. sudo chown -R <username> /data/db (Replace <username> with your username which you can get by typing whoami in the terminal)
7. mongod

Got to localhost:8000.

[Sammy0807]

After the mern blog appears the first time, once I refresh the page, I get a typeError: cannot read property ‘map’ of undefined On client/modules/post/components/postlist.js 10:9