Observables and operators

Up until this point, we’ve used observables as a way to capture the data that came from the backend API using the subscribe method, but let’s take a step back and ask what an observable is and why we don’t just use JavaScript promises.

Let’s use a table to organize our explanation:

	Single	Multiple
Synchronous	Function	Iterator
Asynchronous	Promise	Observable

Table 9.1 – Types of objects by requirement

When we need to perform synchronous processing and expect a return value, we use a function. If we need a collection of synchronous values, we use an object of the Iterator type. We use promises when we need the return value of a function, but its processing is asynchronous...