Unidirectional data flow (or sometimes referred to as reactive programming or functional programming) is often seen as this new trend in frontend applications development brought by React and Flux (or by ReactiveX from Netflix). So many developers think using one of these libraries or frameworks is necessary to start with this pattern. This, of course, is not true. I can use React and don’t have an unidirectional data flow at all, and the opposite, I can use stacks not designed with functional reactive programming in mind and still have an unidirectional data flow.