So far, when writing these subscribe functions, we haven't returned anything. It is possible return an unsubscribe function from a subscribe function. In this lesson we will see how to allow observers to subscribe and unsubscribe from an Observable.
There are many operators available, and in order to understand them we need to have a simple way of communicating how they transform a source Observable into a result Observable over time. To show this we use Marble Diagrams to easily explain what is happening. Throughout this course we are going to see the so-called marble diagrams.