https://www.valentinog.com/blog/redux/

There are two key points for avoiding mutations in Redux:

• Using concat(), slice(), and …spread for arrays .
• Using Object.assign() and …spread for objects .
  Redux protip: the reducer will grow as your app will become bigger. You can split a big reducer into separate functions and combine them with combineReducers

Redux itself is a small library (2KB). The Redux store exposes a simple API for managing the state. The most important methods are:

• getState for accessing the current state of the application
• dispatch for dispatching an action
• subscribe for listening on state changes