TypeScript Changes in Redux v5.0.0: What You Need to Know

Anton Ioffe - January 4th 2024 - 9 minutes read

As the ever-evolving landscape of web development marches forward, the quintessential state management library Redux has stepped into a new era with its v5.0.0 release, fully embracing the robust capabilities of TypeScript. In the following deep dive, we're pulling back the curtain on the significant TypeScript-oriented transformations within Redux. From meticulous codebase conversions to a thorough TypeScript typings overhaul and the adoption of best practices, we'll dissect the strategic impact on your current and future Redux projects. Prepare to navigate the migration pathways, engineer more maintainable and type-safe applications, and peer into the crystal ball of Redux's TypeScript-laden horizon. Whether you’re contemplating an upgrade or starting a new project, this article is your beacon through the shifting tides of Redux's latest typescript-centric incarnation.

TypeScript Conversion and Codebase Impact

The conversion of Redux's codebase to TypeScript represents a significant milestone in enhancing code maintainability. TypeScript's static typing brings about increased predictability and safer refactoring, vital for a widespread library like Redux. For maintainers, TypeScript overlays a structured type system that catches errors at compile time, reducing potential runtime issues. Additionally, it streamlines contribution processes as the codebase becomes more introspective, with types documenting the library's intended use cases directly in the code.

One inherent concern with TypeScript is its potential performance implications, primarily during development. However, these overheads are confined to the build process, and by the nature of TypeScript being a superset of JavaScript, the runtime performance in a production environment remains unaffected. TypeScript may even yield indirect performance gains by enabling developers to write more efficient, error-free code due to its type-checking capabilities.

Developers looking to adapt existing JavaScript Redux projects to the new TypeScript paradigm will need to strategize their migration. A gradual adoption is facilitated by TypeScript's ability to coexist with JavaScript, allowing developers to incrementally annotate and refactor their codebases. Introducing TypeScript types for state and actions is a good starting point, followed by the implementation of stronger types for reducers and middleware, which can now receive enhanced type safety and better support for asynchronous actions in Redux.

Nevertheless, the shift to TypeScript is not without its complications. Common coding mistakes include assuming existing JavaScript types would seamlessly align with TypeScript definitions and underestimating the nuances of TypeScript's type inference and compatibility with dynamic Redux patterns. Correcting such errors involves rigorous type definition and the careful application of TypeScript's utility types, ensuring that the Redux store's shape and behavior remain consistent with the expectations of the type system.

Developers must also consider the compatibility of any third-party middleware and enhancers with the TypeScript-converted Redux. By prioritizing packages that are already compatible with TypeScript and seeking out or contributing to DefinitelyTyped definitions for the rest, developers can ensure that their codebase remains robust and enjoys the full advantages of TypeScript's type safety across their entire Redux application stack. This approach not only aligns with modern development practices but also fortifies the codebase against future updates and potential breaking changes within the Redux ecosystem.

Redux 5.0.0 TypeScript Typings Overhaul

With the release of Redux 5.0.0, the TypeScript typings have seen a significant overhaul aimed at enhancing type safety and addressing previous limitations. A major change is the deprecation of the AnyAction type in favor of UnknownAction. The AnyAction type was a catch-all that included a type string and handled any additional fields as any, which undermined the type safety that TypeScript aims to provide. The introduction of UnknownAction, which treats all non-type fields as unknown, pushes developers to create explicit type guards. For instance, using Redux Toolkit's action creators, you can perform type-safe operations as shown below:

import { createAction } from '@reduxjs/toolkit';

const todoAdded = createAction('todos/todoAdded', (text: string) => {
  return { payload: { text } };

function handleAction(someUnknownAction: UnknownAction) {
  if (todoAdded.match(someUnknownAction)) {
    // 'someUnknownAction' is now typed as `PayloadAction<{ text: string }>`
    console.log(`Todo added with text: ${someUnknownAction.payload.text}`);

The Middleware type in Redux has also been revised. Previously, it made unsafe assumptions about the types of the next and action parameters, with next being typed based on dispatch extensions and action presumed to be a known action. These assumptions often led to typing conflicts in composite Middleware scenarios. Now, with both next and action typed as unknown, developers are encouraged to perform explicit type checking to ascertain the arguments' actual types, as demonstrated here:

const exampleMiddleware: Middleware = (storeApi) => (next) => (action) => {
  if (todoAdded.match(action)) {
    // Processing for 'todoAdded' action
  // Continue to the next middleware
  return next(action);

Another important change is the removal of the PreloadedState type. The updated approach allows direct specification of the preloaded state shape through generic parameters of the Reducer type, facilitating better integration with the API and a more precise type inference.

import { createStore, combineReducers } from 'redux';

interface TodoAppState {
  todos: Todo[];

const rootReducer = combineReducers({ /* reducers */ });

const store = createStore(rootReducer, {
  todos: [{ text: 'Learn Redux 5.0', completed: false }]
} as TodoAppState);

By adapting to these enhancements, developers can achieve a more robust type safety mechanism within Redux applications. Nonetheless, it remains critical to understand and properly implement these changes to truly benefit from the stronger TypeScript integration provided in Redux 5.0.0. How are you planning to adapt the new UnknownAction type and the revised Middleware typing in your projects, and what patterns will you establish to maintain type safety?

Adopting Best Practices with TypeScript in Redux

To fully leverage TypeScript in Redux v5.0.0, it's imperative to establish clear types for your application's state, actions, and reducers. This begins with explicitly declaring interfaces or type aliases that describe the shape of your Redux store and the actions it can handle. By doing so, you ensure your reducers and other Redux-related code will take full advantage of TypeScript's type-safety features.

Utilizing Redux Toolkit eases defining these types. It provides functions like createAction and createSlice, which infer the payload type and automatically associate actions with reducers, respectively. This not only avoids the manual work of linking actions with reducers but also minimizes the chance of typing errors.

Consider this improved code example that illustrates managing user profiles within an application using createSlice:

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

interface UserProfileState {
  entities: UserProfile[];
  loading: boolean;

interface UserProfile {
  id: string;
  name: string;
  email: string;

const initialState: UserProfileState = { entities: [], loading: false };

const userProfileSlice = createSlice({
  name: 'userProfile',
  reducers: {
    profilesLoading: state => {
      state.loading = true;
    profilesReceived: (state, action: PayloadAction<UserProfile[]>) => {
      state.entities = action.payload;
      state.loading = false;
    clearProfiles: state => {
      state.entities = [];
      state.loading = false;

export const { profilesLoading, profilesReceived, clearProfiles } = userProfileSlice.actions;

Selectors are another area where TypeScript's type safety shines. Always use strongly typed selectors to secure the expected return type, ensuring the reliability of your Redux state within components. This is illustrated by pairing createSelector with TypeScript types as shown here:

import { createSelector } from '@reduxjs/toolkit';
// Assume RootState has been defined elsewhere and includes `userProfile` state.

const selectUserProfileState = (state: RootState) => state.userProfile;
const selectUserEntities = createSelector(selectUserProfileState, userProfile => userProfile.entities);

// Usage within a component with `useSelector` hook
// const userProfiles = useSelector(selectUserEntities);

Precise type definitions for action payloads and state slices are crucial for maintaining type safety. They allow TypeScript to enforce strict type checking and help surface errors during compilation rather than at runtime.

Lastly, reducers must uphold Redux's principle of state immutability. Although direct state mutation can elude TypeScript's checks, Redux Toolkit, alongside Immer used within createSlice, offers a safer state update mechanism. This ensures reducer functions act immutably yet appear intuitive. It's a demonstration of Redux Toolkit's capability to champion best practices in a TypeScript environment while enhancing developer experience.

Real-World Scenarios: Migrating to Redux 5.0.0 with TypeScript

When migrating to Redux 5.0.0 with TypeScript, developers should be aware of several refactoring steps crucial for aligning with the new version. The replacement of createStore is a significant change, moving towards configureStore provided by Redux Toolkit, which configures the store with recommended defaults for most applications.

// Before: Using createStore (now deprecated)
import { createStore } from 'redux';
const store = createStore(rootReducer, preloadedState, enhancer);

// After: Adopting configureStore from Redux Toolkit
import { configureStore } from '@reduxjs/toolkit';
const store = configureStore({
    reducer: rootReducer,
    middleware: (getDefaultMiddleware) => getDefaultMiddleware().concat(customMiddleware),

Correctly handling action types is crucial in TypeScript to ensure code quality and avoid type errors. In TypeScript, action types are explicitly defined as strings, which was the conventional approach even in JavaScript, but TypeScript enforces this practice and provides advanced type checking.

// Ensuring action type is always a string

With TypeScript, creating precisely typed actions and selectors becomes more robust. The Redux Toolkit offers utility functions like createAction and createSelector for auto-generating action creators and selectors with type inference that significantly mitigate potential type inconsistencies.

import { createAction, createSelector } from '@reduxjs/toolkit';

// Action with inferred type for the payload
const updateUser = createAction<User>('user/update');

// Selector with precise return type
const selectUser = createSelector(
    (state: RootState) => state.user,
    (user) => user

Reducers should be updated to utilize the specific action creators for accurate type inference. This practice provides better type safety than the previously used AnyAction and facilitates the maintenance of reducers by having explicit typings for each action.

import { updateUser } from './actionCreators';

// Utilizing action creators for typing instead of AnyAction
function userReducer(state: UserState = initialState, action: ReturnType<typeof updateUser>): UserState {
    switch (action.type) {
        case updateUser.type:
            // The payload's type is inferred
            return { ...state, ...action.payload };
            return state;

For middleware, TypeScript requires explicit type annotations, which increases type safety during runtime. Middleware types can become complex, and Redux Toolkit's type improvements help in specifying exact behavior.

import { Middleware } from '@reduxjs/toolkit';

// Middleware with explicit type annotations for enhanced type safety
const loggerMiddleware: Middleware = storeApi => next => action => {
    console.log('dispatching', action);
    let result = next(action);
    console.log('next state', storeApi.getState());
    return result;

These changes not only assist developers in smoothly transitioning to Redux 5.0.0 but also harness the prowess of TypeScript for a more reliable and maintainable codebase. Embrace these refactorings, test incrementally, and appreciate the strides in type safety and improved developer experience that come with Redux's new iteration.

Future-Proofing Redux Applications with TypeScript

TypeScript's integration into Redux provides development teams with robust tools to ensure the structural integrity and maintainability of their state management logic. With TypeScript's focus on type safety, it can facilitate nuanced representations of application state and predict the types of actions that can modify such state. A practical application of this might involve leveraging TypeScript's utility types to create conditional types that can handle complex state transitions with ease.

Imagine enhancing the clarity of Redux state with TypeScript's utility types:

// Conditional types to represent complex state transitions
type LoadingState<T> = {
    status: 'loading';
    data: null;
    error: null;
} | {
    status: 'succeeded';
    data: T;
    error: null;
} | {
    status: 'failed';
    data: null;
    error: Error;

type UserState = LoadingState<User[]>;

In this scenario, the LoadingState utility type assists developers in managing asynchronous operations commonly encountered in modern web applications, ensuring that type safety extends across the entire state management process.

Redux Toolkit's compatibility with TypeScript provides a clear path for type-safe action creators. The toolkit's createAsyncThunk is an excellent example of a function already available that leverages TypeScript to precisely type both arguments and return values, ensuring actions comply with defined types.

Here's how you would use Redux Toolkit's createAsyncThunk with TypeScript:

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

// Type-safe asynchronous action creator
const fetchUserData = createAsyncThunk<User, string, { rejectValue: Error }>(
    async (userId, { rejectWithValue }) => {
        try {
            const response = await userService.fetchUserById(userId);
            return response.data;
        } catch (err) {
            return rejectWithValue(err instanceof Error ? err : new Error('An unknown error occurred'));

In the example above, fetchUserData is a type-safe action creator, which is a real-world implementation of TypeScript principles in Redux, contributing to more predictable state management behaviors.

TypeScript's type system can be complemented by the immutable update patterns encouraged by Redux Toolkit, which leverages Immer under the hood. This synergistic use of TypeScript and Immer prevents common mutation mistakes that can occur when handling the state directly.

Consider the following reducer that demonstrates an immutable update pattern with TypeScript:

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

type PostState = {
    byId: Record<string, Post>;
    allIds: string[];

const initialState: PostState = {
    byId: {},
    allIds: []

const postSlice = createSlice({
    name: 'posts',
    reducers: {
        addPost: (state, action: PayloadAction<Post>) => {
            const post = action.payload;
            state.byId[post.id] = post;

export const { addPost } = postSlice.actions;

The createSlice function from Redux Toolkit allows us to define reducers and associated actions with TypeScript typing support, maintaining immutability without directly mutating the state.

Finally, TypeScript and Redux together can improve the maintainability and evolutionary potential of state management. The clear typing of actions and state shapes paves the way for straightforward refactoring and feature addition. Future advances in TypeScript, such as more powerful mapped types or enhancements to type inference, could provide Redux developers with even more tools for concise and error-free coding.

As TypeScript continues to evolve, Redux developers may explore further synergies, expanding the toolkit to seamlessly handle an even broader range of state management scenarios with elevated type safety, ensuring that future Redux applications are built with a solid foundation.


The article delves into the changes introduced in Redux v5.0.0 with regards to TypeScript, highlighting the benefits of static typing in terms of code maintainability and error prevention. It explores the impact of TypeScript conversion on the codebase, the typing overhaul in Redux v5.0.0, and best practices for using TypeScript in Redux. The article emphasizes the need to strategize migration and ensure compatibility with third-party middleware. A challenging technical task for the reader could be to refactor their existing Redux codebase to incorporate TypeScript and optimize type safety by utilizing explicit type annotations for actions and state, adopting Redux Toolkit for enhanced productivity, and creating precise type definitions for selectors and reducers.

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