Redux makes it possible to store all statuses in an application in a single place, which is called a store. A store is the intermediary to all of the changes of the status of the app. Using Redux, a component cannot communicate directly with another component; instead, the changes always go through a single source, which is an action. Redux can be described simply by three fundamental principles. Those three main principles, which will be briefly explained in this chapter, are summarized as follows:

• A single source of truth
• The read-only nature of the state
• The reducer principle

The whole application state is stored in a single object, called the state tree. This makes it easier to create modern applications, as the server state can easily be serialized and hydrated to client apps.

An example for an online medical store app is as follows:

Emitting an action is the only way to change the state of a Redux app. Views cannot directly write to the state tree. In Redux, every intent needs to dispatch actions, which tell the reducers (a function) to transform the state. Mutating the state is also not recommended; hence, every time, the reducers write the existing state object with the new version:

The transformation logic of the state tree is specified with the use of pure functions, called reducers. Reducers are special functions that take the current state and action to return a new state, without mutating the state.