Breaking Changes in Redux v5.0.0: A Guide for Developers

Anton Ioffe - January 4th 2024 - 10 minutes read

In the ever-evolving landscape of web development, staying updated with the latest changes in cornerstone libraries is critical for maintaining a competitive edge. Redux, as a pivotal state management tool, has undergone significant transformation with its landmark v5.0.0 release. In this article, we'll meticulously peel back the layers of Redux's latest iteration, delving into strategic alterations and enhancements that stand to redefine your development workflow. From the seismic shift towards TypeScript optimization to the retirement of familiar paradigms, we'll guide you through mastering the subtle art of adapting to these changes. Whether it's reshaping your type system approach, leveraging the power of new features, or navigating revised syntax with finesse, this comprehensive guide is your beacon through the Redux v5.0.0 metamorphosis, poised to unlock new potentials in your modern Redux development endeavors.

Understanding the Redux v5.0.0 Evolution: The Shifts and Nuances

Redux v5.0.0 heralds a substantial shift towards TypeScript utilization, a move initiated by the community's drive for stronger typing and enhanced developer safety. The commitment to TypeScript conversion started back in 2019 but sat dormant owing to apprehensions about compatibility with the existing ecosystem. Now with v5.0.0, Redux is fully constructed from its TypeScript-converted source. This change aligns Redux with modern development practices, offering developers the power of static typing which can preemptively eliminate a plethora of runtime errors. Yet, it's likely that the tighter type constraints may expose previously undetected type errors in existing code, nudging developers to tidy up type definitions to comply with v5.0.0's stricter regimen.

Another pivotal transformation in Redux v5.0.0 is the dual module packaging system that embraces the ECMAScript Module (ESM) specification while maintaining backward compatibility with CommonJS (CJS). The concerns that motivated this were manifold: a desire for future-proofing Redux as the JavaScript ecosystem migrates towards ESM, and a nod to performance improvements through tree-shaking and faster load times possible with modern bundlers. Developers can now import from Redux using either module system, but it's crucial to consider that depending on the target environment and toolchain, one might face necessary configuration tweaks to ensure seamless interoperation of ESM and CJS modules.

Regarding the ESM/CJS upgrades, Redux v5.0.0 introduces the main build artifact as an ESM file (redux.mjs), while still including a conventional CJS build for projects not ready to transition to ESM. This adjustment brings Redux up to speed with the latest JavaScript module trends and offers improved import/export syntax, which is more tree-shaking friendly and conducive to static analysis. The shift to ESM might require adjustments in how projects are built and bundled, which, though initially daunting, likely results in leaner and more performant application bundles.

Specifically pertaining to Redux's tooling, the switch to employing tsup for builds incorporates a modern bundler that outputs ESM and CJS artifacts, including source maps. Such tooling decisions emphasize the Redux team's commitment to developer experience by simplifying debugging and facilitating smoother source code transitions. Improved tooling, combined with the adoption of ES2020 features like optional chaining and object spread, makes the Redux codebase more modern and elegant, inviting developers to write cleaner and more expressive code.

The evolution of Redux with v5.0.0 improves the library in terms of performance and modularity. Developers must now deepen their understanding of TypeScript and module systems. Recognizing that there is effort required for integration challenges and codebase updates, this migration promises a more robust, maintainable, and future-proof environment for Redux applications. It propels projects towards an optimized architecture that stands resilient in the face of the evolving JavaScript landscape.

Mastering String-Only Action Types and Deprecated createStore

The recent enforcement of string-only action types in Redux v5.0.0 marks a significant change, reinforcing the best practice that actions in Redux should be serializable. This requirement primarily aims to facilitate a more readable action history within Redux DevTools, offering developers a clearer debugging process. One of the immediate effects is the exclusion of non-string action types, such as Symbols, which were previously leveraged by some legacy codebases for action type definitions. This shift towards string-only types serves to standardize action structures, simplifying the mental model for actions in Redux but also adding a layer of rigidness that requires developers to refactor existing code that doesn't comply.

// Before Redux v5.0.0 - Symbol action types could be used
const MY_ACTION = Symbol('MY_ACTION');
function actionCreator() {
    return { type: MY_ACTION };

// After Redux v5.0.0 - Action types must be strings
function actionCreator() {
    return { type: 'MY_ACTION' };

The shift away from Symbols might necessitate a significant refactor of action types across the codebase, directly impacting modularity and complicating the reusability of certain libraries or middlewares previously built with non-string action types. The emphasis on string-only types, while enhancing serialization and readability, introduces a rigid constraint that, while generally seen as a small step for most codebases, may present larger hurdles for those few with deep investments in the formerly permissible patterns.

Simultaneously, Redux's deprecation of the createStore method nudges developers toward configureStore from Redux Toolkit, thus promoting a more feature-rich and out-of-the-box experience for managing Redux logic. Although the deprecation does not imply immediate removal or operational obsolescence—legacy code reliant on createStore will continue to work—it introduces a visual stroke that serves as a gentle prompt for developers to transition to modern practices.

// Deprecated: createStore
import { createStore } from 'redux';
const store = createStore(reducer);

// Recommended: configureStore from Redux Toolkit
import { configureStore } from '@reduxjs/toolkit';
const store = configureStore({ reducer });

The choice to continue using the deprecated createStore method might result in a codebase that gradually falls behind contemporary conventions. Opting for the alias legacy_createStore maintains the status quo without the visual cue of deprecation, but the recommended path is full adoption of configureStore. This method abstracts setup complexity, incorporates essential middleware by default, and aligns with the Redux community's best practices. The introduction of such deprecations, although subtle, signals a move toward unifying the Redux ecosystem under the Redux Toolkit, simplifying future maintenance and scalability of Redux-based applications.

Given these developments, consider the following questions: how will the enforcement of string-only action types streamline your action management and debugging routines? In what ways might the createStore deprecation notice encourage or hinder you to move toward configureStore and the benefits of Redux Toolkit? Reflect on your current Redux setup and evaluate the potential impacts both changes could have on your app's architecture and developer experience.

Type System Overhaul: Embracing UnknownAction and Middleware Adjustments

The transition from AnyAction to UnknownAction signifies a major step forward in enhancing type safety within Redux v5.0.0. With AnyAction, the flexibility to annex any field to an action and assume its presence was convenient but suboptimal for enforcing strong types. UnknownAction, on the other hand, establishes a rigorous typology, mandating developers to perform explicit type checks.

// Adjusted approach with UnknownAction leveraging Redux Toolkit's match method
import { MiddlewareAPI, Dispatch } from 'redux';
import { todoAdded } from './actionCreators';

const myMiddleware = (store: MiddlewareAPI) => (next: Dispatch) => (action: unknown) => {
    if (todoAdded.match(action)) {
        console.log(action.payload); // Type-safe property access
    return next(action);

Migration to UnknownAction demands a paradigm shift within middleware, abandoning the notion of prescriptive knowledge about action shapes. Implementing type guards such as someActionCreator.match(action) brings clarity and precision to action handling by asserting the specific structure of actions, which underpins predictable and accurate state transitions.

// Example middleware adjustment for UnknownAction
import { MiddlewareAPI, Dispatch } from 'redux';
import * as ActionCreators from './actionCreators';

const myMiddleware = (api: MiddlewareAPI) => (next: Dispatch) => (action: unknown) => {
    // Utilizing match methods provided by action creators as type guards
    Object.values(ActionCreators).forEach(actionCreator => {
        if ('match' in actionCreator && actionCreator.match(action)) {
            console.log(action.payload); // Access to typed payload
            // Other relevant middleware logic can follow here
    return next(action);

Adapting to UnknownAction places a premium on building in comprehensive type checks. This move towards explicit type confirmation aligns state management practices with static type discipline. For those accustomed to strongly-typed languages, these changes will resonate as a prudent evolution. Developers must now diligently perform runtime type verification to sidestep potential slip-ups, like assuming property existence that is indiscernible to TypeScript.

The omission of mandatory type checks exemplifies a common error in this evolutionary phase, risking interface with properties on action objects that TypeScript can no longer implicitly identify. To correct this, developers should conduct assiduous runtime type checks to curb unexpected behaviors. These modifications in Redux's type system prompt introspection on the balancing act between preserving the approachability of Redux and maintaining a precise and explicit application typology.

Incorporating these type system amendments may moderately impact the performance and complexity of Redux applications—requiring more upfront type checks can add slight overhead. Nevertheless, the benefits of heightened type safety and improved predictability in state management outweigh these concerns. By fostering stricter adherence to type constraints, Redux v5.0.0 caters to a more modular and reusable codebase, bolstering maintenance and scalability for the long-term.

Leveraging New Features for Modern Redux Development

Redux v5.0.0 introduces dynamic reducer injection with its injectReducer functionality, providing a robust solution for code-splitting and incremental loading of reducers. This feature allows developers to add reducer logic on-the-fly, which supports use cases like loading logic for a feature when it is accessed by the user, consequently optimizing initial load times and resource utilization.

import { configureStore, combineReducers } from '@reduxjs/toolkit';
import userReducer from '../features/users/userSlice';

const store = configureStore({
  reducer: {
    users: userReducer

// Adding a dynamic injectReducer function to the store for reducer code-splitting
store.asyncReducers = {}; // Initial object to hold asynchronous reducers

store.injectReducer = (key, asyncReducer) => {
  store.asyncReducers[key] = asyncReducer; // Register the async reducer
  store.replaceReducer(createRootReducer(store.asyncReducers)); // Update the root reducer

// Helper function to combine static and asynchronous reducers
function createRootReducer(asyncReducers) {
  return combineReducers({
    users: userReducer,

// Example usage of injectReducer when the 'posts' feature is accessed
import postsReducer from '../features/posts/postSlice';

store.injectReducer('posts', postsReducer);

The modularization enabled by injectReducer imparts greater modularity in code organization. However, managing dynamic reducers must be approached with cognizance to avoid excessive complexity and to ensure reducers' initialization and disposal are handled correctly.

When it comes to middleware handling, Redux encourages setting up middleware during the initialization of the store. It is essential to declare all middleware logic using the configureStore function from Redux Toolkit, which simplifies the store configuration and leverages middleware effectively. This structured setup prevents the potential pitfalls of attempting to dynamically alter middleware, which can introduce unpredictable behaviors and maintenance challenges.

With these advancements, it becomes even more crucial for developers to consider how best to structure and maintain their Redux store. Effective implementation of dynamic reducers can lead to improved lazy loading of state logic, aiding in scaling applications gracefully. Nevertheless, awareness of the common mistake of improperly initializing reducers or modifying store middleware after creation is paramount. A recommended best practice includes leveraging thorough unit tests and integration tests to ensure that the dynamic aspects of state management remain robust and error-free.

Developers are invited to reflect on the integration of Redux v5.0.0's features such as injectReducer to enhance code-splitting while preserving the integrity of the Redux store. Thoughtful application of these updates enriches the development process with an expanded toolkit for managing state in complex applications while maintaining Redux’s commitment to simplicity and predictability.

In the latest update of Redux v5.0.0, the traditional object syntax for extraReducers in createSlice has been deprecated in favor of a preferred builder callback pattern. The builder pattern enhances type inference and code maintainability, encouraging developers to migrate existing code. During this transition, it is crucial to refactor createSlice implementations as shown in the following example:

const todosSlice = createSlice({
  name: 'todos',
  initialState: { todos: [] },
  reducers: {
    addTodo(state, action) {
  extraReducers: builder => {
    builder.addCase(fetchTodos.fulfilled, (state, action) => {
      state.todos = action.payload;

Adhering to the updated practices avoids the common mistake of using the now-deprecated object syntax. Embracing the builder callback not only aligns code with the current version of Redux but also simplifies future upgrades and maintenance.

The shift to typing actions and middleware parameters as unknown in configureStore is a proactive measure to enforce safer type-checking practices in Redux. Gone are the days of presuming all actions to be of known types. To integrate this change, middleware should incorporate explicit type verifications, including the use of the PayloadAction type from Redux Toolkit:

const typeCheckedMiddleware = store => next => action => {
  if (myActionCreator.match(action)) {
    // Confirm the action matches the action creator's type
    const typedAction = action as PayloadAction<MyPayload>;
    // Proceed with your middleware logic here, using typedAction
  // Action is forwarded to the next middleware
  return next(action);

This middleware snippet demonstrates prudent use of type assertions, promoting robust handling of unknown actions within the Redux system. Implementing such strong type checks preserves the store’s integrity, safeguarding against unintended mistakes from incompatible action types.

While leveraging the builder callback for reducers and the stricter middleware types, developers should ponder the implications for their code structures. It is essential to willingly tackle type-management issues and evaluate middleware to dismiss any lingering implicit type assumptions. As you delve into Redux v5.0.0's type enhancements, consider the essence of your actions and middleware. How will they adapt to these enforced type constraints, and what measures will be adopted to ensure a seamless transition?


The article "Breaking Changes in Redux v5.0.0: A Guide for Developers" explores the significant changes in Redux's latest iteration, v5.0.0, and provides a comprehensive guide for developers to adapt to these changes. The key takeaways include the shift towards TypeScript utilization, the dual module packaging system, the enforcement of string-only action types, the deprecation of createStore in favor of configureStore, the transition from AnyAction to UnknownAction for enhanced type safety, and the introduction of new features like dynamic reducer injection. The article challenges developers to reflect on how these changes will streamline their development workflow and encourages them to consider restructuring their Redux store while leveraging the new features to enhance code organization and modularity.

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