React. Today, because it's awesome, but I'm also exited about its development (like fiber).

Relay 2 (not yet released), which claims to introduce a lot of new features (like local state management, think something like flux/redux) and better performance (more details: https://speakerdeck.com/wincent/relay-2-simpler-faster-more-...). If the team behind Relay 2 were to deliver even 50% of those claims, it'd be fantastic.

Functional programming - I was introduced to it on university, it was ok but I wasn't raving about it. What's funny to me, JS made me love FP and before React I really hated JS and looked at it as a toy language.

Scala - I'm only learning it but it's fascinating and learning it broadens my general CS knowledge.