Reactive Programming is an event-driven programmation based on the observer / subscriber pattern via an event loop.
They are reactive implementing a reactor pattern.
It means that:
In another word, a change of state is propagated to the system where functions can react to them.
Some backend example events are:
Some frontend example events are:
In an imperative programming setting, the expression a:=b+c would mean that a is being assigned the result of b+c in the instant the expression is evaluated, and later, the values of b and c can be changed with no effect on the value of a.
On the other hand, in reactive programming, the value of a is automatically updated whenever the values of b or c change, without the program having to re-execute the statement a:=b+c to determine the presently assigned value of a.
Reactive Application are event-driven data application.
Example of reactive / event driven data application:
Most reactive system are implemented via an event loop.
https://www.reactivemanifesto.org/ 1)