I am in the same boat as you. Though web development is not my primary job, this is how I learn it in my spare time. Would love to hear from others.

a) Learn fundamentals and working of JS (right from event loop), How modern browsers works as full blown runtime, single page applications, Functional programming paradigm etc.

b) Be able to categorize and put opensource I come across frequently, into problem buckets they solve. Started with libraries, frameworks and tools and am going one level down now

c) How massive development is now possible on browser side with kind of tooling available

d) Picked up Angular and Node for "Hello World" and some small apps for learning

e) I follow related subreddits like- r/Javascript, r/AngularJS, r/webdevelopment etc and of course lurk on HN