In order to learn JS you should grasp the event loop. Once you learned to think async, being able to write queues, limit concurrency, etc its just different flavours of syntax and ES6 is mostly syntatic sugar. If you are a web dev you should learn the basic web APIs and avoid libraries and frameworks at all cost. Dont use React until you have written a web component without it. Also if you are a web dev, learn CSS its very simple and powerful once you understand that a rule below overides a rule above, and a more specific rule overides a less specific rule.