Redux is a predictable state container for JavaScript apps.
It helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test.

On top of that, it provides a great developer experience, such as live code editing combined with a time traveling debugger.

The three principles of Redux are:

1. Single source of truth
The state of your whole application is stored in an object tree within a single store.

2. State is read-only
The only way to change the state is to emit an action, an object describing what happened.

3. Changes are made with pure functions
To specify how the state tree is transformed by actions, you write pure reducers.

1. Predictable state management
2. Centralized state management
3. Easy to debug
4. Easy to test
5. Easy to maintain
6. Easy to scale
7. Easy to integrate with other libraries
8. Easy to integrate with server side
9. Easy to integrate with native apps

Yes, you can use Redux with other libraries like Angular, Vue, etc.
Because Redux is a state management library, it can be used with any other library or framework.

Redux Toolkit is the official, opinionated, batteries-included toolset for efficient Redux development.
It is intended to be the standard way to write Redux logic.

Features of Redux Toolkit:

1. Configure Store
2. Create Slice
3. Create Async Thunks
4. Create Async Hooks
5. Create Async Entities
6. Create Async Queries
7. Create Async Mutations

In simple terms, Flux is an application architecture for React utilizing a unidirectional data flow.

Flux has multiple stores, one for each domain of the app.

Flux is an application architecture for React utilizing a unidirectional data flow.

Redux is a predictable state container for JavaScript apps.

Flux and Redux are both unidirectional data flow architectures.
The main difference between them is that Redux uses a single store to hold the state of the entire application.

Flux has multiple stores, one for each domain of the app.

A reducer is a pure function that takes the previous state and an action, and returns the next state. (previousState, action) = newState

/* reducer example */
export const reducer = (state = initialState, action) => {
  switch (action.type) {
    case "ACTION_TYPE":
      return {
        ...state,
        property: action.payload,
      };
    default:
      return state;
  }
};

Actions are payloads of information that send data from your application to your store.
They are the only source of information for the store. You send them to the store using store.dispatch().

/* action example */
export const action = (payload) => {
  return {
    type: "ACTION_TYPE",
    payload,
  };
};

The store is the object that brings them together. The store has the following responsibilities:

• Holds application state
• Allows access to state via getState()
  You can retrieve the current state of the Redux store by calling getState().
• Allows state to be updated via dispatch(action)
  The only way to update the state is to emit an action, an object describing what happened. You can send actions to the store by calling dispatch(action).
• Registers listeners via subscribe(listener)
  The store allows you to register listeners via the subscribe method. The listeners are called whenever an action is dispatched, and some part of the state tree may potentially have changed.
• Handles unregistering of listeners via the function returned by subscribe(listener)
  The subscribe method returns a function for unregistering the listener.

Redux Thunk is a middleware that allows you to write action creators that return a function instead of an action.

The thunk can be used to delay the dispatch of an action, or to dispatch only if a certain condition is met. The inner function receives the store methods dispatch and getState as parameters.

Middleware provides a third-party extension point between dispatching an action, and the moment it reaches the reducer.

It is a way to extend Redux with custom functionality. Middleware lets you wrap the store's dispatch method for fun and profit.

The key feature of middleware is that it is composable. Multiple middleware can be combined together, where each middleware requires no knowledge of what comes before or after it in the chain.

Redux ships with a applyMiddleware() function to facilitate the use of middleware.

Constants are used to define action types. They are used to avoid typos and duplication when writing action types.

They are also used to keep the naming consistent between different parts of the codebase.

You can use the connect() function to connect a React component to a Redux store.

The connect() function connects a React component to a Redux store.

/* connect example */
const mapStateToProps = (state) => {
  return {
    property: state.property,
  };
};

const mapDispatchToProps = (dispatch) => {
  return {
    action: (payload) => dispatch(action(payload)),
  };
};

export default connect(mapStateToProps, mapDispatchToProps)(Component);

You can create a Redux store using the createStore() function.

/* create store example */
const store = createStore(reducer);

You can create a Redux action using the createAction() function.

/* create redux action example */
export const action = (payload) => {
  return {
    type: "ACTION_TYPE",
    payload,
  };
};

You can dispatch actions from a React component using the useDispatch() hook.

/* dispatch action example */
const dispatch = useDispatch();
const action = (payload) => {
  return {
    type: "ACTION_TYPE",
    payload,
  };
};

dispatch(action(payload));

You can handle asynchronous actions in a Redux application using the redux-thunk middleware.

The redux-thunk middleware allows you to write action creators that return a function instead of an action. The thunk can be used to delay the dispatch of an action, or to dispatch only if a certain condition is met.
The inner function receives the store methods dispatch and getState as parameters.

/* thunk asynchronous actions example */
export const action = (payload) => {
  return (dispatch) => {
    dispatch({ type: "ACTION_TYPE", payload });
  };
};

You can split a Redux application into multiple reducers and combine them using the combineReducers function.

/* combine reducers example */
const rootReducer = combineReducers({
  reducer1,
  reducer2,
  reducer3,
});

You can test a Redux application using a library such as redux-mock-store.

The redux-mock-store library allows you to create a mock Redux store that you can use to test your Redux actions and reducers.

/* redux mock store example */
const store = mockStore(initialState);

Redux DevTools is a live-editing time travel environment for Redux with hot reloading, action replay, and customizable UI. It provides power-ups for your Redux development workflow.

Redux DevTools is a set of packages that can be used to monitor and debug your Redux application. It is available as a browser extension for Chrome, Firefox, and Edge, as well as a standalone app for macOS, Windows, and Linux.

Redux DevTools features are as follows:

These are the main differences between Redux and React Context API:

Redux is a predictable state container for JavaScript applications.

It helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test.

On top of that, it provides a great developer experience, such as live code editing combined with a time traveling debugger.

Every Redux applications has these components:

• Containers
  

  Containers are components that are connected to the Redux store. They are responsible for reading part of the state tree and injecting it into their child components as props.

• Actions
  

  Actions are payloads of information that send data from your application to your store. They are the only source of information for the store. You send them to the store using store.dispatch().

• Reducers
  

  Reducers specify how the application's state changes in response to actions sent to the store. Remember that actions only describe what happened, but don't describe how the application's state changes.

• Store
  

  The store is the object that brings them together. The store has the following responsibilities:

Redux forms are a set of reducers and actions to create and manage form state in Redux.

You can use Redux forms to manage the state of your form and keep track of the values of the inputs in your form.

You can use the redux-form library to implement Redux forms in your application.

You can implement server-side rendering with a Redux application using the react-redux-universal-hot-example project.

The react-redux-universal-hot-example project is a boilerplate application that demonstrates how to implement server-side rendering with a Redux application.

/* server side rendering example */
import { Provider } from "react-redux";
import { createStore } from "redux";
import { renderToString } from "react-dom/server";
import { StaticRouter } from "react-router-dom";

const store = createStore(reducer);

const html = renderToString(
  <Provider store={store}>
    <StaticRouter location={req.url} context={{}}>
      <App />
    </StaticRouter>
  </Provider>
);

You can handle complex state management in a Redux application using the Immer library.

The Immer library allows you to work with immutable state in a more convenient way. It is based on the copy-on-write mechanism.

/* nested object state example */
const initialState = {
  property1: {
    property2: {
      property3: "value",
    },
  },
};

export const reducer = (state = initialState, action) => {
  switch (action.type) {
    case "ACTION_TYPE":
      return {
        ...state,
        property1: {
          ...state.property1,
          property2: {
            ...state.property1.property2,
            property3: action.payload,
          },
        },
      };
    default:
      return state;
  }
};