The best if you learn and practice the following four libraries and frameworks: React, Ember.js, Angular, Vue. You will see different concepts and you gonna be a real professional frontend dev. For example, you can create a simple interface or widget with React, but if you have to develop a complex big web application, Ember or Angular is a better choice. Most of these frameworks have great support, community and matured. Learning Ember is so easy as React: http://yoember.com