Before learning any framework or React, It'll help you alot if you understand atleast these 12 concepts of javascript.
1. let & const
2. Understanding Classes,Objects, Properties and Methods
3. Understanding Arrow Functions
4. Arrays & Array Methods
5. Reference and Primitive Types
6. The Spread & Rest Operator
7. Destructuring
8. Modules (Exports and Imports)
9. Asynchronous Code & Promises
10. Template Literals
These are just the bare minimum foundation of javascript you must grasp, there are alot more to learn than this small list.