Observables, Observers, and Subjects

Observables and subscribers are at the base of reactive programming. We can say that they are the building blocks of reactive programming. In the previous two chapters, you already got a glimpse of Observables and subject. We observed on data with observable/subject instances; but that's not all we want; instead, we want to get all the actions and data changes reactively into the observable instances, making the application completely reactive. Also, while reading the previous chapters, you may have wondered how exactly does it operate? In this chapter, let's have a foundation of the pillars of reactive programming—Observables, Observers, and subjects:

• We will look into details of transforming various data sources to observable instances
• You will learn about various types of Observables
• How to use Observer instances and subscriptions, and, lastly, subjects and their various implementations

We will also learn about various factory methods of Observable.

There's a lot to understand in this chapter, so let's start with understanding Observables first.