In Chapter 4, Creating Actions, we examined Flux actions in detail—action creator functions in particular. One aspect of action creators we didn't cover was asynchronous behavior. Asynchronicity is central to any web application, and in this chapter, we'll think about what this means for a Flux architecture.
We'll start by covering the synchronous nature of Flux, as breaking this synchronicity breaks the whole architecture. Next, we'll dive into some code that makes API calls and some action creators that need to synchronize multiple API calls before actually dispatching the action. Then, we'll introduce promises as return values from action creator functions.