While the Reactive Manifesto helps us understand the characteristics of a Reactive System, it does not really help with understanding how Reactive Systems are built. To understand this, we will consider the traditional approach to building a simple use case and compares it with the reactive approach.

The use case we want to build is a stock price page that displays the price of a specific stock. As long as the page remains open, we want to update the latest price of the stock on the page.