The Flux project is in maintenance mode and there are many more sophisticated alternatives available (e.g. Redux, MobX, Recoil) and we would recommend using them instead.
What is Flux?
Flux is the application architecture that Facebook uses for building client-side web applications.
What does it do?
It complements React's composable view components by utilizing a unidirectional data flow.
How do I use it?
It's more of a pattern rather than a formal framework, and you can start using Flux immediately without a lot of new code.