Introduction

Before you get into the meat of Angular 2 Observables, it is important to first understand the problem you are trying to solve.

A frequently encountered scenario in software is where you are expecting some entity to broadcast that something happened; let's call this an "event" (distinct from a browser event). You would like to hook into this entity and attach behavior to it whenever an event occurs. You would also like to be able to detach from this entity when you no longer care about the events it is broadcasting.

There is more nuance and additional complexity to Observables that this chapter will cover, but this concept of events underscores the fundamental pattern that is useful to you as the developer.

The Observer Pattern

The Observer Pattern isn't a library or framework. It is just a software design pattern upon which ReactiveX Observables are built. Many languages and libraries implement this pattern, and ReactiveX is just one of these implementations; however, ReactiveX...