ESM/CJS Compatibility in Redux v5.0.0: Impact on Development

Anton Ioffe - January 7th 2024 - 10 minutes read

As the web development landscape surges forward with its ever-evolving technologies, Redux v5.0.0 stands at the confluence of change, having extended its embrace to harmonize the two prevalent module systems, ECMAScript Modules and CommonJS. In this deep-dive analysis, we'll navigate the nuanced realities of this duality, dissecting its influence on performance and code organization within the rich ecosystem of Redux. We'll chart the course through practical refactoring patterns, sidestep common interoperability blunders, and cast a discerning eye toward Redux's modular horizon. This is an essential expedition for seasoned developers seeking to harness the full potential of Redux in the rapidly shifting tides of modern web development.

Embracing Hybrid Module Syntax in Redux v5.0.0

Redux v5.0.0's embrace of both ECMAScript Modules (ESM) and CommonJS (CJS) reflects a nuanced understanding of the current JavaScript development milieu. With the introduction of the exports field in package.json, developers are now furnished with a robust mechanism for module resolution, guiding bundlers and environments to choose the appropriate module format seamlessly. This change implies that import statements in a developer's code might resolve differently under varying conditions, yet without extra cognitive load, thanks to the behind-the-scenes resolution logic. For instance, import { createStore } from 'redux' will automatically resolve to the ESM version in an environment that supports it, while falling back to the CJS counterpart where necessary.

The strategy Redux employs for integrating mixed modules is delicate and deliberate. With both redux.mjs and a traditional CJS entry point available, developers can work within their preferred syntax without significant alteration to their established workflows. When importing from Redux, there is no longer the need to specify the module format, as import and require statements within consumer code function as usual, with the underlying resolution abstracted away. However, attention is required when interfacing with hybrid modules, since developers must ensure that named exports are consistently referenced, regardless of the module system being used.

Namespace conflicts present a potential for confusion in a dual-format module ecosystem. In Redux v5.0.0, careful consideration has been given to namespace consistency across both ESM and CJS formats to avoid such issues. Consistent export naming ensures that whether developers are destructuring imports or accessing properties on a require-imported object, their reference to Redux entities remains the same. This eliminates the risks of namespace discrepancies leading to runtime errors or silent failures in code execution.

Within this hybrid context, export statements in Redux have been standardized to maximize the interoperability of modules. The use of named exports where possible favors explicitness and treeshaking efficiencies, while still allowing users the choice to define their module boundaries. For instance, when contributing middleware using CJS, it is understood that module.exports will correspond to default when imported into an ESM-oriented codebase. Additionally, interop helpers like interopRequireDefault may be required to ensure compatibility when importing a module that does not natively support ESM.

Redux v5.0.0 exemplifies a judicious approach to adopting modern JavaScript practices while ensuring backward compatibility is not compromised. This transition encourages developers to be mindful of how import declarations, such as import { createStore, combineReducers } from 'redux', behave in diverse environments. It fosters a community where careful coding practices and an understanding of the underpinnings of the module syntax are essential. Correct usage of named imports is paramount in maintaining the delicate balance Redux strikes with its support for mixed module syntax.

Performance Implications of ESM/CJS Coexistence

By adopting dual module systems, Redux v5.0.0 has positioned itself at the intersection of cutting-edge JavaScript and backward compatibility, resulting in intriguing performance implications. The transition towards ESM artifacts enables optimizations like tree-shaking, a technique that eliminates unused code from the final bundle. Tree-shaking benefits from the static nature of ESM because bundlers can determine at build time which exports are never imported and safely remove them. This tighter bundle optimizes loading times and reduces the initial payload size, which is particularly useful for complex applications with numerous dependencies.

However, while ESM encourages a leaner bundle through tree-shaking and static analysis, the coexistence with CJS adds a layer of complexity. Ensuring backward compatibility inherently entails a certain architectural overhead, sometimes mandating additional code or wrappers to serve both module types. Consequently, this may lead to a somewhat paradoxical scenario where gains from tree-shaking could be partially negated by the weight of CJS compatibility layers. Analyzing real-world Redux applications reconfigured for v5.0.0, some saw a negligible increase in bundle size, suggesting that in practice, the concern may be more theoretical than impactful, yet it underscores the need for careful engineering.

Lazy loading, a pivotal performance optimization practice, shifts with the ESM/CJS coexistence as well. Utilizing ESM's dynamic import() function facilitates asynchronous module loading, beneficial for large applications that prioritize faster initial load times. The deterministic nature of ESM module resolution enables more predictable performance benchmarks compared to the dynamic requires in CJS. As an illustration, a Redux store with ESM-exported selectors demonstrates how code splitting can substantially reduce the main bundle size, making initial loads quicker and subsequent functionality loads demand-based.

// Example of an ESM-exported selector with dynamic import for lazy loading
export const selectUser = state => state.user;

// Example of dynamically importing the selector in an application component
const UserComponent = async () => {
    const { selectUser } = await import('./selectors');
    // Utilize the selector here

The exhaustive performance profiling of Redux v5.0.0 reveals real-world impacts on loading efficiency. Benchmarks highlight that ESM facilitates quicker startup times due to static imports over CJS's dynamic resolution mechanisms. In measured scenarios, applications loading ESM-formatted Redux modules demonstrate accelerated resolution and execution, which is particularly paramount for enhancing user experience with improved interactivity and responsiveness.

The subtleties of integrating ESM with legacy CJS systems remind developers that the applauded benefits of ESM format, such as bundle size reduction and improved lazy loading, are not automatic. Ensuring that toolchains are up-to-date and properly configured is paramount. Misconfigurations or outdated tooling can hinder the ESM's potential, leaving anticipated performance boosts on the table. As such, updating and optimizing build systems is not merely a technical task but a strategic move to fully exploit the performance benefits Redux v5.0.0 promises in the modern web landscape.

Refactoring Patterns for Compatibility and Efficiency

Refactoring Redux codebases for ESM/CJS compatibility under Redux v5.0.0 requires a discerning approach to the traditional patterns, especially in the context of store creation. The shift from createStore to configureStore of Redux Toolkit signals a movement towards a more structured configuration setup and an implicit embrace of Redux best practices. The middleware and enhancers support, although not automatic, are set to sensible defaults that accommodate most application needs, while still allowing for customization. Such refactoring enriches the codebase with patterns that streamline state management and configuration transitions.

// Before: Using createStore with an explicit middleware setup
import { createStore, combineReducers, applyMiddleware } from 'redux';
import rootReducer from './reducers';
import thunk from 'redux-thunk';
const store = createStore(rootReducer, applyMiddleware(thunk));

// After: Refactored to use configureStore with Redux Toolkit's defaults
import { configureStore } from '@reduxjs/toolkit';
import rootReducer from './reducers';
const store = configureStore({
  reducer: rootReducer,
  // Middleware and other configurations can be explicitly modified here if needed

The introduction of TypeScript in Redux v5.0.0 necessitates the incorporation of types into the refactoring process. Adhering to TypeScript's strict type safety is instrumental in reducing bugs and enhancing developer understanding of state flow. With this perspective, refactored code should make use of TypeScript's capabilities for clearer and more maintainable code.

// Before: Classical Redux pattern without TypeScript
function addUser(state, user) {
    return {
        users: [...state.users, user]

// After: Leveraging Redux Toolkit with TypeScript
import { createAction, createReducer } from '@reduxjs/toolkit';

interface User {
  id: number;
  name: string;

const userAdded = createAction<User>('users/userAdded');

const usersReducer = createReducer<User[]>([], {
    [userAdded.type]: (state, action) => {
        state.push(action.payload); // Mutable update with immer

Refactoring complex logic, such as API call status management, can be optimized using TypeScript along with Redux Toolkit's creators. Utility functions and type-safe actions ensure consistency and clarity in state updates, reducing boilerplate and redundancy.

// Using a utility function to handle status updates with TypeScript
import { createAction, createReducer, PayloadAction } from '@reduxjs/toolkit';

interface UserState {
  users: User[];
  status: 'idle' | 'loading' | 'succeeded' | 'failed';

const fetchUserRequest = createAction('users/fetchUserRequest');
const fetchUserSuccess = createAction<User[]>('users/fetchUserSuccess');
const fetchUserFailure = createAction('users/fetchUserFailure');

const initialState: UserState = { users: [], status: 'idle' };

const usersReducer = createReducer(initialState, (builder) => {
        .addCase(fetchUserRequest, state => { state.status = 'loading'; })
        .addCase(fetchUserSuccess, (state, action: PayloadAction<User[]>) => {
            state.status = 'succeeded';
            state.users = action.payload;
        .addCase(fetchUserFailure, state => { state.status = 'failed'; });

A clean separation of store configuration from store creation is pivotal in maintaining adaptability in the face of module system changes. Decoupling setup from application logic by exporting store configuration enhances module interoperability and readies the application for updates in the Redux ecosystem.

// Separating store configuration for modularity with TypeScript
import { configureStore } from '@reduxjs/toolkit';
import rootReducer from './reducers';

export type AppState = ReturnType<typeof rootReducer>;

export const store = configureStore({
    reducer: rootReducer,
    // Additional store setup and configuration can go here

By adopting TypeScript and the enhanced capabilities of Redux Toolkit, developers enable modularity, reusability, and a greater degree of type safety in state management. This solid foundation fosters a codebase capable of evolving with technological progress, ensuring that applications remain resilient and maintainable amidst the dynamic shifts in modern web development practices. Careful consideration is necessary to manage these changes, with an eye towards preserving efficiency and compatibility across module systems.

Overcoming Common Mistakes in Module Interoperability

Developers transitioning to Redux v5.0.0's ESM/CJS paradigm might inadvertently mix named and default exports incorrectly. A common mistake occurs when a Redux reducer is exported as a default in an ESM file but incorrectly imported with named syntax in a consuming CJS module. Here's how to do it right:

// reducer.js (ESM)
export default function reducer(state = initialState, action) {
    // reducer logic

// store.js (CJS)
const reducer = require('./reducer').default;

The require statement specifically accesses the default export of the ESM-based reducer, acknowledging the difference in export semantics across module systems.

Configuring bundlers such as Webpack can also stump developers unfamiliar with the intricacies of mixed module environments. Incorrect configuration can lead to errors or bloated bundles due to missed tree-shaking opportunities. For Webpack, it's vital to set the module.rules appropriately and specify output.environment to include { module: true } for ESM output format. Within your Webpack configuration, always ensure the resolve.extensions array is accurately configured to prioritize .mjs files for ESM support.

Another oversight in ESM/CJS interoperability is the mishandling of inter-module dependencies and potential side-effects. When working within ESM, it's crucial to understand that importing named exports binds to live variables, and inadvertently triggering side-effects might affect shared state across modules. Use caution when re-exporting CJS dependencies in ESM files as it could lead to unintended consequences.

// CJS module that might cause side-effects
module.exports = {
    performAction: () => {
        sideEffectFunction(); // Potential side-effect

// ESM module that re-exports a CJS module
export { performAction } from './cjsModule';

Ensure that exported functions are pure and free of side-effects when performing such re-exports to maintain predictable behavior across your application.

Finally, a lack of understanding of how ESM handles asynchronous importing can result in sub-optimal code. The import() function's proper use not only encourages code splitting but also aligns with modern JavaScript's dynamic import capabilities. Remember that import() returns a promise that resolves to the module:

// ESM syntax for dynamically loading a module
import('path/to/module').then(module => {
    // Use the dynamically imported module
    // This ensures module is loaded and its exports are ready to use

By focusing on these aspects and becoming vigilant about the subtleties of ESM/CJS compatibility, developers can navigate the complexities involved and craft well-structured Redux applications.

The Future-Proof Redux: Predicting Evolutions in Module Patterns

Amidst a ceaseless progression of JavaScript module system evolutions, Redux's middleware landscape is on the cusp of transformation. With the embrace of ESM's static structures, developers have the opportunity to advance middleware design, envisioning a scenario where side-effect management and asynchronous workflows become more context-aware. Envision modular middlewares dynamically loaded to suit specific portions of the application state, thereby aligning resources with real-time application needs. This slimmed-down approach promises a leaner, more efficient application lifecycle, with the ability to load only the necessary capabilities on demand, thus fine-tuning performance and memory usage in complex applications.

The Redux API surface will not remain untouched by the paradigm shift toward module systems. There's potential for the API to evolve into a more granular array of modular functionalities. Developers could then handpick the parts of Redux they need, scaling their usage with application complexity and avoiding the burden of an all-encompassing library load. This modular sensation could offer developers the luxury of a lighter cognitive load, where choosing what to include resembles picking tools from a well-organized toolbox rather than lugging around the full set for every job.

The Redux community's input will guide these advancements, ensuring that the changes resonate with practical development needs. As the Redux team delicately balances progressive ESM integration with CJS compatibility, community feedback will shape the resulting framework, ensuring that the advancements are not just theoretically sound but battle-tested through real-world usage. This feedback loop allows Redux to stay adaptable and responsive to the diverse environments JavaScript developers operate in.

The repercussions of Redux's journey into ESM and CJS compatibility may inspire novel development patterns that ripple through the JavaScript ecosystem. Will Redux shape itself to fit into the modern JavaScript landscape, or will it, more ambitiously, sculpt that very landscape with the modularity and enhanced developer experience it brings forth? This new chapter could beckon a redefinition of best practices for state management, embodying adaptability and modularity as its new pillars, in contrast to the monolithic architectures of Redux's past.

Developers must astutely navigate the shifting tides of JavaScript modules and Redux's adaptation to remain ahead. The innovations in state management patterns prompted by changes in the JS ecosystem could compel the reinvention of Redux itself. As JavaScript and adjacent technologies like React progress, Redux's relevance in particular use cases may wax or wane. Developers vigilant to these trends will discover opportunities to implement more elegant state management solutions, ensuring their craft remains as resilient and relevant as the applications they build.


The article explores the impact of ESM/CJS compatibility in Redux v5.0.0 on modern web development. It discusses the benefits and challenges of incorporating both module systems and provides insights into performance implications, refactoring patterns, and overcoming common mistakes. The key takeaway is the need for developers to be mindful of import declarations and to update and optimize build systems to fully exploit the performance benefits of Redux v5.0.0. A challenging task for the reader would be to refactor their Redux codebase to leverage Redux Toolkit and TypeScript, enhancing modularity and type safety in state management.

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