We just finished our last chapter that taught us more about what operators exist and how to utilize them effectively. Armed with this knowledge, we will now go into this subject in more depth. We will go from learning about what parts exist, to actually understanding the nature of RxJS. Knowing the nature of RxJS involves understanding more about what makes it tick. To uncover this, we need to cover topics such as what the differences are between hot, warm, and cold Observables; knowing about Subjects and what they are good for; and the sometimes ignored topic of Schedulers.

There are also other aspects of working with Observables that we want to cover, namely, how to deal with errors and how to test your Observables.

In this chapter, you will learn about:

• Hot, cold, and warm Observables
• Subjects: how they differ from Observables, and when to use them
• Pipeable operators, a recent addition to the RxJS library, and how they affect how you compose Observables
• Marble testing, the testing machinery in place that helps you with testing your Observables