Chapter 2
Deep in the Sequence

I have childhood memories of playing a puzzle video game in which you had to guide a falling stream of water across the screen using all kinds of tricks. You could split the stream, merge it back later, or use a tilted plank of wood to change their direction. You had to be creative to make the water reach its final goal.

I find a lot of similarities between that game and working with Observable sequences. Observables are just streams of events that we transform, combine, and query. It doesn’t matter whether we’re dealing with simple Ajax callbacks or processing gigabytes of data in Node.js. The way we declare our flows is the same. Once we think in streams, our programs become simpler.

In this chapter we focus on how to effectively use sequences in our programs. So far we’ve covered how to create Observables and do simple operations with them. To unleash their power, we have to know to translate our program inputs and outputs into sequences that carry our program flow.

Before we get our hands dirty, we’ll meet some of the basic operators that will help us start to manipulate sequences. Then we’ll implement a real application that shows earthquakes happening in (almost) real time. Let’s get to it!