A lot of juniors make the mistake of choosing breadth first. But there's so much breadth involved in making a modern web app that if you go for breadth it'll ta

A lot of juniors make the mistake of choosing breadth first. But there's so much breadth involved in making a modern web app that if you go for breadth it'll take you a decade to get to be good enough at anything for someone else to trust you to do it without micromanagement (i.e. To be mid-level instead of junior). At the beginning you need only as much breadth as is required to survive with your stack. It's ok for entire other sections to be black boxes ("we get requests from the front end in JSON and we process the request this way return other JSON and somehow <hand wave> it gets rendered"). After that you want to work on depth until you can work on a single part of the stack (pick back end, front end, or sysadmin/ops) without help or supervision. To get there, you may need to even focus on understanding one site feature and its technologies and concepts at a time. You may need to spend multiple years on this first portion of the stack before hitting mid-level competency with it. That's totally normal. Once you've gained the competency to work independently in one area, you're ready to increase your breadth again: pick another part of the stack and do a deeper dive there.