What is Reactive programming?

Unlike imperative programming (IP) or (Object-Oriented Programming) OOP, where we write our code in terms of the order of lines or statements, in Reactive programming (RP), we write the code or programs in terms of events.

In simpler words, RP means writing programs using events, or RP means writing programs that define how to react to events. As we discussed, events are changes in the state of the program or application. So we can also define RP as follows:

Reactive programming is a kind of programming paradigm to that propagates changes.

Let's discuss one of the important and frequently used RP examples (almost all books or tutorials use the same scenario). Consider the following example of a spreadsheet application:

Observe that the A3 cell has a formula =A1+A2, that is, A3 is the sum of the values of the cells A1 and A2.

Initially, A3 has a value of 0. When we change the value of cell A1 or A2, or both, the spreadsheet updates the value of A3:

We can observe that the cell A3 is updated with 3 automatically; this is Reactive programming.