Keep learning JavaScript, React, and then add on at least Nodejs. Node is a great and easy JavaScript Backend language that will make you a full-stack developer. Being full-stack is not only powerful when looking for a job, but helps you get a complete picture of the development lifecycle of a product. Obviously knowing HTML, CSS, and basic tools like Git will help as well.
Totally Agree with the will and having some knowledge about databases also will be helpful as a full-stack developer.