I was trying to put FullCalendar 2.1.1 but it is not working:
For anyone coming across this, there was only one solution working for me. I'm using webpack to compile my scripts and nothing was working for me, no matter what order I had require('fullcalendar') placed in my main.js file.
I had to downgrade to version 3.4.0. It instantly solved the problem.
npm install --save fullcalendar@3.4.0