Go Vanilla. Did you ever try to write a whole page without any framework? Just HTML, CSS and JS, keeping each of them clean and separated (no CSS in JS, no JS on HTML, etc.)? Make it work on Safari 10, IE11, Edge, FF 35+ and Chrome 45+? Make sure it still looks good on smartphones? Check if it is progressive? And then, once everything works, optimize the whole thing using a build pipeline? Because that's the kind of stuff I have to deal with. I have been coding for 10+ years, and I still learn something new every day just by doing that.
If you think that's easy, then we can start talking about code architecture and tools. What kind of architectures, patterns and algorithms do you know? What's a dirty flag? A builder pattern? Do you know OOCSS? BEM? What's the difference between
<strong>? How to do ARIA? How to XOR-encrypt (shuffle bits)?
If you know all that, then try to do something completely different. Go learn Rust and write a simple game of Pong or Snake, using OpenGL 4+. Just doing that will throw you into a whole new world of ideas and concepts which you can also use as a web dev.
Once you tried out all of that, you should probably not be a junior anymore and you will keep on growing with projects you do.
Also, don't forget to stay online, read blogs and questions and write answers. By talking about what you know, you can get others to confirm or correct your knowledge, which expands your horizon and makes you a better dev passively. In my time on Hashnode, I learned a lot just by writing answers like this one. The community here is awesome, so I recommend it wholeheartedly.