Working with asynchronous JavaScript
Because of the architecture of React Native (more on this in Chapter 3, Hello React Native) and the typical use cases of apps, understanding asynchronous JavaScript is crucial. A typical example of an asynchronous call is a call to an API.
In a synchronous world, after making the call, the application would be blocked until the answer from the API is received. This is, obviously, unexpected behavior. The application should respond to user interaction while it waits for the response. This means the call to the API has to be done asynchronously.
There are multiple ways of working with asynchronous calls in JavaScript. The first one is callbacks.
Exploring callbacks
Callbacks are the most basic way to work with asynchrony in JavaScript. I would recommend using them as little as possible, because there are better alternatives. But since a lot of libraries rely on callbacks, you have to have a good understanding of them.
