What is your advice about how to become an an excellent fullstack developer?

Question

I want to become an expert in:
- Front-end: JavaScript/HTML/CSS
- and Back-end: Java, SQL

Besides learning and writing those languages as much as possible, what else do I have to do to become an expert developer?

Answer 1

- Expert Debugging skills [It's relatively tougher in front-end]

- Unit testing/ End to end testing

- In practical scenarios you got to work on codes developed by others, so understanding the basic architecture and flow of code, different paradigms to write the code is necessary. This comes with experience.