I want you to consider the following program and think about the output logged in the console,
Is it 11 or 21? As most of you would guess correctly, the answer would be 11. That’s because, once the value of b is computed, it is no longer dependent on the value of a. As a result, changing the value of a does not change the value of b.
Suppose the value of a changes over time, e.g., it may be a user input from a webpage that can be modified by the user anytime. And we want b to be calculated as soon as a is changed. A new programming paradigm called Reactive Programming is used for such problems.
An example of Reactive Programming would be a spreadsheet. If you have used it before, you know that when you write a formula for a cell like “=A1+B1″, the value of the cell gets modified as soon as the value in either cell A1 or cell B1 is modified.
Let us now modify our example using Reactive Programming. The value of a is going to change every 3 sec, and as soon as it does, b will be modified. The resulting reactive program is following: