I won't say what framework I already know because I want to avoid bias. Ideally, I'd like to know suggestions on the best over-all framework to learn going forward.
Of course, consider front-end or back-end first, but I'll assume you are open to either.
I'm currently learning Play (scala) because the framework is a part of two projects I've been involved with at my current job.
I was learning Mercury.js because we selected it for a project, mostly because I wasn't a fan of Flux, but having said that, the community has voted for React, so I'll be moving to get more experience with React (we're not re-writing the Mercury stuff, but I probably won't recommend it for future projects, BUT, if you're not familiar with Mercury.js, check it out, I really like it).
I'm assuming you're already down either the Less or Sass road, so I'd look for the next thing in CSS, which just might be https://github.com/css-modules/css-modules
For testing, I'd check out Tape (unit tests) and nightwatch.
Make sure you're up on Webpack and/or Browserify
Oh the list goes on and on.
Out of curiosity, you mention web development framework, but do you have any interest in IoT? and would you want to use your web-dev skills in interfacing with hardware? The reason I ask is I've been building a framework which hopefully will allow web-devs to develop embedded code. I'd be keen to hear your feedback.
I would love to check out what you're doing. This is exactly my profile, web-dev pivoted to IoT(embedded) engineering