The UI is the visual equivalent of data (the state) along with interactive controls to change that state. The UI fires actions, which leads to the change in state. Side effects are external operations that are triggered due to some state change. There are observers in the system that look out for certain state changes and perform the corresponding side effects.

The data flow triad of Action --> State --> UI, coupled with side effects, creates a simple mental model of the UI. MobX strongly adheres to this mental model and you can see that reflected in its API, with observables, actions, reactions, and observers. The simplicity of this API makes it easy to tackle some of the complex interactions in UI.

If you have used Redux before, you can see that MobX reduces the ceremony needed to cause a state change and handle side effects. MobX strives to provide a declarative and reactive API for state management without compromising on simplicity. Throughout this book, this philosophy of MobX will be explored, with a deeper look at its API and real-world use cases.

In the next chapter, we will dive into the world of MobX with a first hand look at its core building blocks.