Best Practices for Migrating to Redux Toolkit 2.0 from Legacy Redux

Anton Ioffe - January 10th 2024 - 10 minutes read

Welcome to the strategic roadmap for revitalizing your state management architecture as we delve deep into the transformative journey of migrating to Redux Toolkit 2.0. Senior developers, prepare to unlock the most efficient pathways and practices that will not only ease the transition from the legacy Redux implementation but will also leverage the cutting-edge enhancements introduced in this robust iteration. From refactoring core reducers and actions with precision, to harnessing the power of RTK Query for optimized data fetching, our comprehensive guide is your architect's blueprint to modernizing your workflow. Join us as we explore the intricate melding of middleware mechanics and TypeScript fortifications to elevate the precision and maintainability of your codebase, equipping you to navigate the evolving landscape of modern web development with confidence.

Leveraging Redux Toolkit 2.0 Features for Efficient Migration

Redux Toolkit 2.0 introduces a comprehensive set of features aimed at simplifying and expediting the transition from legacy Redux setups. One of the pivotal elements for seamless migration is the enhanced configureStore function which replaces the traditional createStore. This new configuration method automatically sets up the store with good defaults such as the Redux DevTools Extension and thunk middleware. Migrating to configureStore is straightforward, with developers needing only to replace:

const store = createStore(rootReducer);


const store = configureStore({
    reducer: rootReducer,

This upgrade equips the store with modularity and allows for a more efficient integration of additional middleware or enhancers.

In managing state, combineSlices emerges as a significant upgrade in Redux Toolkit 2.0, streamlining the process of code-splitting and reducer injection. By enabling dynamic injection of slice reducers, applications can load just the necessary parts of the state as and when required, which is particularly beneficial in large-scale applications. This feature not only helps in minimizing initial load times but also supports on-demand scaling. It acts as a flexible alternative to Redux's combineReducers function, elegantly combining slices without explicit registration at the store's creation.

Within the createSlice function, Redux Toolkit 2.0 has improved support for selectors—a mechanism that has always been crucial in Redux for accessing and deriving data from the state. Utilizing auto-generated selectors that are inherent to each slice significantly reduces the need to write repetitive selector functions. The availability of memoized selectors further enhances performance by preventing unnecessary re-renders, thus ensuring that components are only updated when the relevant slice of the state changes. This is especially vital for maintaining optimal application performance as the state shape becomes more complex.

Moreover, the new version encourages modular and reusable API surfaces that bolster the transition from legacy practices. By employing the createSlice API, developers can encapsulate reducers and associated action creators within independently manageable slices of state. This not only aligns with modern JavaScript best practices but also substantially reduces boilerplate. Developers can now define the initial state and corresponding reducers in a concise manner, thereby simplifying the management and scalability of application state.

Migratory Patterns for Reducer and Action Refactoring

Refactoring legacy Redux reducers and actions to utilize createSlice in Redux Toolkit 2.0 begins with a systematic evaluation of your existing reducers. In the process of transitioning from traditional switch-case reducers to the object-map methodology of createSlice, it's crucial to carefully reinterpret each logic block held within the previous cases. Observe how a classic switch-case reducer is reworked:

// Legacy switch-case reducer
function counterReducer(state = 0, action) {
  switch (action.type) {
    case 'INCREMENT':
      return state + 1;
    case 'DECREMENT':
      return state - 1;
      return state;

// Transformed with createSlice
const counterSlice = createSlice({
  name: 'counter',
  initialState: 0,
  reducers: {
    increment: state => state + 1,
    decrement: state => state - 1,

The builder pattern in createSlice has replaced the previously acceptable object syntax for defining extraReducers, significantly improving the maintainability and TypeScript compatibility of your code. Familiarize yourself with methods like .addCase(), .addMatcher(), and .addDefaultCase() to proficiently implement this pattern. Here we juxtapose the deprecated object syntax approach with the newly prescribed builder pattern:

// Deprecated: Object syntax for extraReducers
extraReducers: {
  'external/increment': (state, action) => state + action.payload,
  // Other external action handlers...

// Adopting the builder pattern for extraReducers within createSlice
const externalIncrement = createAction('external/increment');
const counterSlice = createSlice({
  name: 'counter',
  initialState: 0,
  reducers: {
    // Reducer logic here...
  extraReducers: (builder) => {
    builder.addCase(externalIncrement, (state, action) => {
      return state + action.payload;
    // Additional external action handlers...

Migrating to createSlice eschews the need for custom action creators, as action creators are autogenerated. Adjust your dispatch calls to utilize these efficient shortcuts:

// Before: Manually dispatching actions
dispatch({ type: 'INCREMENT' });

// After: Utilizing auto-generated action creators
const { increment, decrement } = counterSlice.actions;

It is vital to confirm all reducers align with immutable update patterns enforced by Immer, avoiding direct object mutations in favor of the declarative update logic supplied by createSlice. Below is an illustration of proper immutable update usage:

// Before: Directly handling immutability
case 'ADD_TODO':
  return [...state, action.payload];

// After: Leveraging Immer for immutable updates in Redux Toolkit
reducers: {
  addTodo: (state, action) => {

Adhering to these modern approaches not only streamlines your codebase but also sets a foundation for a robust, succinct, and easily maintainable application architecture.

Adapting Data Fetching with RTK Query and createAsyncThunk

Replacing traditional Redux data fetching mechanisms with RTK Query and createAsyncThunk marks a significant shift in handling asynchronous operations. RTK Query encapsulates the complexity of managing fetch requests, caching, and re-fetching logic. It simplifies boilerplate significantly by abstracting the need to write custom actions, reducers, or selectors. On the other hand, createAsyncThunk provides a level of granularity in data fetching that can be beneficial for developers who require explicit control over dispatch actions.

When choosing RTK Query, developers gain the advantage of automatic cache handling. This not only improves performance by eliminating unnecessary network requests but also intelligently handles data invalidation. RTK Query's caching mechanism is designed with a heuristics-based approach, thus simplifying the developer's task by handling the data lifecycle. However, the downside of this abstraction layer is reduced control. You rely on RTK Query to decide when and how to fetch data, cache it, and invalidate it, which may not fit all use cases.

In contrast, createAsyncThunk enables developers to define their own fetching logic, specifying exactly when a fetch should occur and how to process the response. This can improve performance by tailoring the logic to specific requirements—which could mean finer control over the use of memory and network resources. Moreover, it ensures that the developer retains direct control over the side effects associated with data fetching actions, which is essential for certain complex scenarios. The trade-off here includes the overhead of maintaining more boilerplate code associated with defining thunks, managing loading states, and error handling explicitly.

Considerations around memory management are also pivotal. RTK Query's built-in cache may hold onto data that is no longer needed if not properly configured, albeit it does attempt to automatically purge stale or unused data. With createAsyncThunk, developers must implement their memory management logic, which could lead to memory leaks if not handled carefully, but it provides the flexibility to finetune memory usage.

Overall, the choice between RTK Query and createAsyncThunk relies on the project's requirements and the development team's preferences. For applications where cached data and automatic refetch are recurrent patterns with standard requirements, RTK Query offers a robust solution. Conversely, if the project demands detailed fetch behavior or involves complex transactions where explicit control is a must, createAsyncThunk would be the more appropriate choice, granting the developer full autonomy at the cost of additional complexity.

Reinforcing Reactive Logic with Middleware and Listeners

The integration of createListenerMiddleware is a watershed moment in the evolution of Redux middleware, representing a shift from more cumbersome, traditional middleware and saga-based approaches to a more straightforward, leaner paradigm of state-driven side effects. This transition has been particularly significant in terms of performance, as the listener middleware simplifies reactive logic by directly responding to specific actions or state changes without the overhead of saga's complex generators or the intricacies of observables. With createListenerMiddleware, developers gain the advantage of creating side effects that are more predictable and easier to manage, while integrating seamlessly within the Redux data flow.

import { createListenerMiddleware, addListener } from '@reduxjs/toolkit';

const listenerMiddleware = createListenerMiddleware();
  actionCreator: someActionCreator,
  effect: async (action, listenerApi) => {
    // Perform side effect here in response to action

As this middleware is inherently designed for subscribing to actions and states, developers can harness the power of reactive programming in their applications with better performance and less boilerplate. For complex asynchronous operations, though, developers must remain vigilant about managing these side effects correctly to prevent potential performance bottlenecks. These include avoiding duplicated listeners, writing efficient side effect functions, and using conditional logic to prevent unintended sprawling of reactive behaviors throughout the application.

Another compelling aspect of adopting createListenerMiddleware is its modular nature, which encourages a more maintainable and organized codebase. Unlike sagas, which often require boilerplate and introduce non-trivial complexity, listener middleware's simplicity makes it amenable to applications where code needs to be broken into more granular and reusable units. Best practices suggest structuring your middleware in a way that actions can be related to their effects in a coherent and easily traceable manner, thereby reducing cognitive overload for developers navigating the code.

// A dedicated file for listener middleware enhances modularity and clarity
import { createListenerMiddleware } from '@reduxjs/toolkit';

export const listenerMiddleware = createListenerMiddleware();

// Export typed hooks to interact with the middleware
export const { startListening, stopListening } = listenerMiddleware;

Another consideration is the choice between using inline anonymous functions versus named effect functions. While inline functions may offer convenience and locality, they may not readily communicate the side effect's intent or enable reuse. Conversely, named functions improve readability and testability, two crucial aspects often compromised in complex asynchronous flows.

const myEffectFunction = async (action, listenerApi) => {
  // Reusable effect logic

  actionCreator: someActionCreator,
  effect: myEffectFunction // Enhancing readability and testability

Lastly, it is crucial to consider error handling while architecting async side effects. Where sagas and observables come with their own error catching mechanisms, the listener middleware mandates a deliberate approach. Developers will need to ensure that errors are not only caught but handled in a way that the application remains robust and that the middleware continues operating effectively.

  actionCreator: someActionCreator,
  effect: async (action, listenerApi) => {
    try {
      // Attempt the side effect
    } catch (error) {
      // Handle errors gracefully

TypeScript Integration and Type-Safe Design in Redux Toolkit 2.0

Redux Toolkit 2.0 introduces a paradigm shift in TypeScript integration, streamlining type-safe design and minimizing the potential for common coding pitfalls. By leveraging the advanced typing solutions in RTK 2.0, developers can construct a more predictable and maintainable codebase. One of the foundational features is the ability to create pre-typed hooks. The useDispatch and useSelector hooks can now be customized to fit the app's root state and dispatch types. This ensures that both your dispatch and selector usages are type-safe throughout the application, reducing the chance of runtime errors due to incorrect types.

// Defining pre-typed hooks
const useAppDispatch = () => useDispatch<AppDispatch>();
const useAppSelector: TypedUseSelectorHook<RootState> = useSelector;

The enhanced reducer type inference in RTK 2.0 mitigates one of the more frequent issues seen in legacy Redux implementations—verbose and manual type declaration. The createSlice utility now implicitly defines action types, payload shapes, and state transformations robustly. This internal handling of types facilitates a more succinct and less error-prone development experience.

// RTK 2.0 boilerplate-free syntax
const mySlice = createSlice({
    name: 'mySlice',
    reducers: {
        myAction: (state, action: PayloadAction<MyPayload>) => {
            // Automatic type inference
            state.myField = action.payload;

Further embracing the type-safe environment, refactoring your codebase to initiate actions becomes significantly more streamlined. Utilizing RTK's action creators automatically generated by createSlice or createAsyncThunk, the need for manually typing each dispatch is entirely eradicated, imparting confidence that action payloads are correct and reducers are receiving what they expect.

// Using the auto-generated action creators

The strong typing principles of TypeScript can also serve as a guardrail against state mutation errors. By enforcing the correct return type for reducers and utilizing the immutable update patterns provided by Immer, which is baked into the createReducer and createSlice utilities, developers are steered away from mutation pitfalls. In cases where explicit state manipulation is needed, TypeScript can bring clarity that the correct immutable operations are being used.

// Immutable update pattern enforced through TypeScript
const myReducer = createReducer(initialState, (builder) => {
    builder.addCase(mySlice.actions.myAction, (state, action) => {
        return {
            myField: action.payload,

Lastly, it's pertinent to address the ability to refactor complex asynchronous logic with RTK 2.0 while maintaining type safety. createAsyncThunk function signatures now imply return types and provide inferential payload and error types to your reducers. This addresses a common source of mistakes, where developers manually manage promise resolutions and rejections within action creators.

// Type-safe asynchronous action
const fetchData = createAsyncThunk<
    MyData, // Return type for the payload creator
    void, // First argument to the payload creator
        rejectValue: MyError // Optional reject type
>('data/fetchData', async (_, { rejectWithValue }) => {
    try {
        const response = await api.fetchData();
    } catch (err) {
        return rejectWithValue(;

By integrating these practices, Redux Toolkit 2.0 aligns seamlessly with TypeScript, promoting an ecosystem where type safety is paramount. It not only improves developer productivity but also reduces the risk of subtle issues increasing as the application scales. Developers are encouraged to ponder—how might type-safety with RTK 2.0 revolutionize the debugging and maintainability of your current projects?


In this article, we explore the best practices for migrating to Redux Toolkit 2.0 from legacy Redux. We discuss how to leverage the new features of Redux Toolkit 2.0, such as the enhanced configureStore function and combineSlices, to streamline the migration process. We also delve into refactoring reducers and actions using createSlice and the builder pattern, as well as adapting data fetching with RTK Query and createAsyncThunk. Additionally, we highlight the importance of reinforcing reactive logic with middleware and listeners, as well as integrating TypeScript and type-safe design in Redux Toolkit 2.0. The challenging technical task for readers is to refactor their legacy Redux reducers and actions to utilize createSlice and the builder pattern, ensuring the code is more maintainable and follows modern best practices.

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