? Redux Toolkit Notes ?

What is Redux?
Redux is a flexible state container for JS apps that manages our application state separately. It manages the application state in a single store, making it easier to handle complex state logic across the entire app.

Why Redux?
In normal flow, we need to do prop drilling to pass states in between components. Some levels don’t need the states here, which is a burden. Also uplifting a state for large medium apps isn’t a scalable solution as it requires structural changes. That’s why we need redux to manage states. All the states here are kept in store and whichever component needs that they can just subscribe to that store. Redux ensures predictable state management, easier debugging, and improved scalability by enforcing a unidirectional data flow.

Core Redux Components:

Action: An object that describes what happened. It typically contains a type and an optional payload. (A command)
Dispatch: A function used to send actions to the store to update the state. (A event occurring)
Reducer: A pure function that takes the current state and an action, then returns a new state. (Function that triggers when action dispatched)

Installing: npm i @reduxjs/toolkit react-redux

Redux Workflow:

Creating a Slice:
A slice is a collection of Redux reducer logic and actions for a single feature. The prepare callback allows US to customize the action payload before it reaches the reducer.

import { createSlice, nanoid } from "@reduxjs/toolkit";

const postSlice = createSlice({
 name: "posts",
 initialState: [],
 reducers: {
   addPost: {
     reducer: (state, action) => {
       state.push(action.payload);
     },
     prepare: (title, content) => ({
       payload: { id: nanoid(), title, content },
     }),
   },
   deletePost: (state, action) => {
     return state.filter((post) => post.id != action.payload);
   },
 },
});

export const { addPost, deletePost } = postSlice.actions;

export default postSlice.reducer;

Creating store:

import { configureStore } from "@reduxjs/toolkit";
import postReducer from "../features/posts/postSlice";

export const store = configureStore({
   reducer: {
       posts: postReducer
   },
 });

Wrap with provider:

import { Provider } from "react-redux";
import { store } from "./app/store.jsx";

createRoot(document.getElementById("root")).render(
 <StrictMode>
   <Provider store={store}>
     <App />
   </Provider>
 </StrictMode>
);

Use in Component:

const PostList = ({ onEdit }) => {
 const posts = useSelector((state) => state.posts);
 const dispatch = useDispatch();

 return (
   <div className="w-full grid grid-cols-1 gap-6 mt-12">
     {posts.map((post) => (
       <div key={post.id}></div>
     ))}
   </div>
 );
};

Redux Browser Extension: Redux DevTools

const store = configureStore({
  reducer: rootReducer,
  devTools: process.env.NODE_ENV !== 'production',
});

Async Operation in Redux (Redux Thunk):

In Redux, asynchronous operations (like API calls) are handled using middleware because Redux by default only supports synchronous state updates. The most common middlewares for handling async operations are Redux Thunk, Redux Toolkit (RTK) with createAsyncThunk, and Redux Saga.

Implementation:

import { createSlice, createAsyncThunk } from '@reduxjs/toolkit';

// Fetch all posts
export const fetchPosts = createAsyncThunk('posts/fetchPosts', async () => {
  const response = await fetch('https://jsonplaceholder.typicode.com/posts');
  return response.json();
});

// Initial State
const initialState = {
  posts: [],
  post: null,
  loading: false,
  error: null,
};

// Slice
const postsSlice = createSlice({
  name: 'posts',
  initialState,
  reducers: {},
  extraReducers: (builder) => {
    builder
      // Fetch all posts
      .addCase(fetchPosts.pending, (state) => {
        state.loading = true;
      })
      .addCase(fetchPosts.fulfilled, (state, action) => {
        state.loading = false;
        state.posts = action.payload;
      })
      .addCase(fetchPosts.rejected, (state, action) => {
        state.loading = false;
        state.error = action.error.message;
      })

      },
});

export default postsSlice.reducer;

Use Case:

import React, { useEffect } from 'react';
import { useSelector, useDispatch } from 'react-redux';
import { fetchPosts, createPost, updatePost, deletePost } from './postsSlice';

const Posts = () => {
  const dispatch = useDispatch();
  const { posts, loading, error } = useSelector((state) =>state.posts);

  useEffect(() => {
    dispatch(fetchPosts());
  }, [dispatch]);

  const handleCreate = () => {
    dispatch(createPost({ title: 'New Post', body: 'This is a new post' }));
  };

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error: {error}</p>;

  return (
    <div>
      <h1>Posts</h1>
      <button onClick={handleCreate}>Create Post</button>
     </div>
  );
};

export default Posts;

Middleware
Middleware in Redux intercepts dispatched actions, allowing for logging, crash reporting, or handling async logic. Middleware lets us customize the dispatch process.

const blogPostMiddleware = (storeAPI) => (next) => (action) => {
  if (action.type === 'posts/publishPost') {
    const contentLength = action.payload.content.length;

    if (contentLength < 50) {
      console.warn('Post content is too short. Must be at least 50 characters.');
      return;
    }
    console.log('Publishing post:', action.payload.title);
  }
  return next(action);
};

const store = configureStore({
  reducer: rootReducer,
  middleware: (getDefaultMiddleware) => getDefaultMiddleware().concat(blogPostMiddleware),
});

Selectors
Selectors help access specific parts of the state.

export const selectCount = (state) => state.counter.value;

Error Handling
Handle errors effectively with proper state management.

import { createSlice, nanoid } from "@reduxjs/toolkit";

const postSlice = createSlice({
 name: "posts",
 initialState: [],
 reducers: {
   addPost: {
     reducer: (state, action) => {
       state.push(action.payload);
     },
     prepare: (title, content) => ({
       payload: { id: nanoid(), title, content },
     }),
   },
   deletePost: (state, action) => {
     return state.filter((post) => post.id != action.payload);
   },
 },
});

export const { addPost, deletePost } = postSlice.actions;

export default postSlice.reducer;

RTK Query (Simplified Data Fetching)

RTK Query simplifies data fetching, caching, and synchronization. RTK Query automatically caches requests and avoids unnecessary refetching, improving performance.

Setting Up RTK Query

import { configureStore } from "@reduxjs/toolkit";
import postReducer from "../features/posts/postSlice";

export const store = configureStore({
   reducer: {
       posts: postReducer
   },
 });

Usage in Components

import { Provider } from "react-redux";
import { store } from "./app/store.jsx";

createRoot(document.getElementById("root")).render(
 <StrictMode>
   <Provider store={store}>
     <App />
   </Provider>
 </StrictMode>
);

Immutable Updates with Immer

Immer allows us to write logic that "mutates" state directly while keeping the updates immutable under the hood.

const PostList = ({ onEdit }) => {
 const posts = useSelector((state) => state.posts);
 const dispatch = useDispatch();

 return (
   <div className="w-full grid grid-cols-1 gap-6 mt-12">
     {posts.map((post) => (
       <div key={post.id}></div>
     ))}
   </div>
 );
};

Mutate vs. Immutable

Mutate: Changing the data directly. For example, modifying an object or array.
Immutable: Instead of modifying data directly, we create a new copy with the changes applied, leaving the original data untouched.

How Immer Works
Immer helps us write code that looks like we're mutating data (i.e., changing it directly), but it automatically keeps the changes immutable under the hood. This is useful for avoiding common bugs when dealing with immutable data structures in JavaScript.
Example: Without Immer (mutation):

const store = configureStore({
  reducer: rootReducer,
  devTools: process.env.NODE_ENV !== 'production',
});

With Immer (immutability):

import { createSlice, createAsyncThunk } from '@reduxjs/toolkit';

// Fetch all posts
export const fetchPosts = createAsyncThunk('posts/fetchPosts', async () => {
  const response = await fetch('https://jsonplaceholder.typicode.com/posts');
  return response.json();
});

// Initial State
const initialState = {
  posts: [],
  post: null,
  loading: false,
  error: null,
};

// Slice
const postsSlice = createSlice({
  name: 'posts',
  initialState,
  reducers: {},
  extraReducers: (builder) => {
    builder
      // Fetch all posts
      .addCase(fetchPosts.pending, (state) => {
        state.loading = true;
      })
      .addCase(fetchPosts.fulfilled, (state, action) => {
        state.loading = false;
        state.posts = action.payload;
      })
      .addCase(fetchPosts.rejected, (state, action) => {
        state.loading = false;
        state.error = action.error.message;
      })

      },
});

export default postsSlice.reducer;

This makes working with Redux (or any state management) easier because we don’t have to clone and update the state manually; Immer does it for us automatically.

Redux Persist:

To persist Redux state across page refreshes, we can integrate Redux Persist. This will store your Redux state in local storage or session storage and reload it when the app is refreshed.

Install:
npm install redux-persist

Implement:

import React, { useEffect } from 'react';
import { useSelector, useDispatch } from 'react-redux';
import { fetchPosts, createPost, updatePost, deletePost } from './postsSlice';

const Posts = () => {
  const dispatch = useDispatch();
  const { posts, loading, error } = useSelector((state) =>state.posts);

  useEffect(() => {
    dispatch(fetchPosts());
  }, [dispatch]);

  const handleCreate = () => {
    dispatch(createPost({ title: 'New Post', body: 'This is a new post' }));
  };

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error: {error}</p>;

  return (
    <div>
      <h1>Posts</h1>
      <button onClick={handleCreate}>Create Post</button>
     </div>
  );
};

export default Posts;

Wrap with Persisit Gate:

const blogPostMiddleware = (storeAPI) => (next) => (action) => {
  if (action.type === 'posts/publishPost') {
    const contentLength = action.payload.content.length;

    if (contentLength < 50) {
      console.warn('Post content is too short. Must be at least 50 characters.');
      return;
    }
    console.log('Publishing post:', action.payload.title);
  }
  return next(action);
};

const store = configureStore({
  reducer: rootReducer,
  middleware: (getDefaultMiddleware) => getDefaultMiddleware().concat(blogPostMiddleware),
});

Optional Enhancements

Use sessionStorage Instead of localStorage:
Change the storage to session-based (clears when the browser closes):

initialState: {
  items: [],
  status: 'idle',
  error: null,
},

.addCase(fetchData.rejected, (state, action) => {
  state.status = 'failed';
  state.error = action.error.message;
});

Selective Persistence:
Only persist specific slices of the state:

import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react';

const api = createApi({
  reducerPath: 'api',
  baseQuery: fetchBaseQuery({ baseUrl: 'https://jsonplaceholder.typicode.com' }),
  endpoints: (builder) => ({
    getPosts: builder.query({
      query: () => '/posts',
    }),
    getPostById: builder.query({
      query: (id) => `/posts/${id}`,
    }),
    createPost: builder.mutation({
      query: (newPost) => ({
        url: '/posts',
        method: 'POST',
        body: newPost,
      }),
    }),
    updatePost: builder.mutation({
      query: ({ id, ...updatedPost }) => ({
        url: `/posts/${id}`,
        method: 'PUT',
        body: updatedPost,
      }),
    }),
    deletePost: builder.mutation({
      query: (id) => ({
        url: `/posts/${id}`,
        method: 'DELETE',
      }),
    }),
  }),
});

export const {
  useGetPostsQuery,
  useGetPostByIdQuery,
  useCreatePostMutation,
  useUpdatePostMutation,
  useDeletePostMutation,
} = api;
export default api;

I have created a simple blog project with react, redux and ant design having CRUD functionality. You can check it out.
Project Link - Redux Blog App

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