In this chapter, we've learned many ways of creating different kinds of Observable instances and other related instances (Observer, Subscriber, Subscription, and Subject). We've been creating them from timers, values, collections, and external sources such as files. Using this knowledge as a base, we can begin building logic, by chaining operations to them. Many of the factory methods introduced here we'll be coming back in the next chapters. For example, we will be building different behaviors using the Observable.create method.

In the next chapter, we'll introduce various operators, which will give us the power to write real logic using the Observable instances. We have already mentioned some of them, such as map() and filter(), but the time has come to look at them in depth.