The Implications of Dropping UMD Builds in Redux v5.0.0

Anton Ioffe - January 3rd 2024 - 10 minutes read

As seasoned developers navigating the ceaseless tides of web development, it's pivotal to keep our sails aligned with the latest advancements—Redux v5.0.0 is no exception. This Version heralds a strategic transition, eschewing the venerable UMD builds in favor of a modern approach tailored with ESM/CJS. This article ventures deep into the heart of this evolution, weighing the intricate balance between performance enhancements and the rigorous world of TypeScript-driven type safety. We critique the practical aspects of refactoring, offering lucid code transformations, and peer into the horizon, contemplating the adaptability required for the future of state management. Prepare to traverse the landscape of Redux's innovations and what they portend for our craft in the vast realm of JavaScript.

Understanding the Shift: Transitioning from UMD to ESM/CJS in Redux v5.0.0

Redux v5.0.0 makes a decisive move by removing Universal Module Definition (UMD) builds and underscoring its commitment to ECMAScript Modules (ESM) and CommonJS (CJS) formats. This transition aligns with the evolving module consumption patterns within the JavaScript ecosystem. The UMD approach, once a pillar for broad compatibility across diverse environments, has given way to the more sophisticated ESM—a module format natively integrated into the JavaScript language, offering significant advantages such as static analysis and treeshaking capabilities, critical for contemporary web development.

With the evolution of web development tooling and workflows, the requirement for UMD has diminished. Developers now favor ESM/CJS due to their superior integration with modern bundlers and transpilers that efficiently handle these formats for production. Redux v5.0.0 reflects this trend by featuring a primary ESM artifact—the redux.mjs file, optimized for the current development landscape. However, acknowledging that script tag usage persists, Redux includes redux.browser.mjs as part of its distribution—a modern ESM artifact designed for loading Redux via script tags directly from CDNs, serving not as a legacy stopgap but as a convenience for those embracing modern ESM in the browser.

This shift towards ESM and CJS ushers in a cultivated developer experience by leveraging existing standards across the JavaScript environment, including Node.js, which has shown a marked preference for ESM. Redux’s updated build artifacts effectively tailor to diverse developer requirements, simultaneously streamlining the overall package structure for ease of maintenance and clarity.

Redux v5.0.0 introduces a significant update to the package definition with the adoption of the exports field in package.json. This field strategically outlines entry points for the packaged modules, thereby guiding module resolutions and ensuring developers are provided with the correct module format automatically. This proactive approach minimizes versioning conflicts and aligns with the continuous drive for efficient module loading strategies.

Finally, with the updated packaging strategy, the Redux team exhibits openness to community engagement, inviting users to rigorously test the new structure and provide feedback. This inclusive stance fosters collaboration, allowing the library to progress while maintaining an accessible pathway for those reliant on older module conventions, thereby striking a balance between innovation and continuity.

Performance and Bundle Optimization Post-UMD

The removal of Universal Module Definition (UMD) builds in Redux v5.0.0 represents a significant step toward modernizing package delivery with an aim to enhance performance and bundle optimization. By prioritizing ECMAScript Modules (ESM), Redux has opened the door for more efficient tree-shaking during the build process. Tree-shaking, a static code analysis feature of ESM-compatible bundlers, eliminates dead code and unused exports from the final bundle. In contrast to the monolithic nature of UMD, which can bloat bundles with unnecessary code, ESM allows developers to include only the parts of Redux that they use, potentially leading to noticeably smaller bundle sizes.

Benchmarking scenarios in real-world applications show that replacing UMD with ESM/CJS modules can reduce the initial load time of web applications. Since ESM supports static imports, module resolution is deterministic and can be optimized by bundlers ahead of time. This contrasts with the dynamic runtime resolutions often found in CommonJS modules, which can incur performance penalties. The shift to ESM modules contributes to quicker module resolution, further speeding up application startup times, a critical factor in user experience and web performance metrics.

However, developers need to be aware that these benefits come with prerequisites. The efficiency of tree-shaking depends on the compatibility of the entire toolchain with ESM. Bundlers like Webpack and Rollup must be properly configured to take full advantage of these optimizations. In some legacy systems or with misconfigured tooling, the expected gains may not materialize, highlighting the importance of understanding and updating build processes to align with the new module formats provided by Redux v5.0.0.

Adopting the ESM/CJS builds also has implications for memory usage. In theory, by importing only the necessary parts of Redux, applications should consume less memory at runtime. ESM's static structure can lead to more predictable memory consumption patterns, compared to the dynamic requires of CommonJS, where entire modules are loaded irrespective of the specific parts used. Notably, these gains in memory efficiency underscore the importance of employing a modular approach when writing Redux logic, leveraging features like selectors and Redux Toolkit's createSlice to minimize runtime overhead.

While the benefits of moving to ESM for developers and end-users are clear in terms of performance and bundle size reduction, it's imperative to monitor these changes in the context of existing applications. Developers must conduct their own benchmarks, observe the impacts of module restructuring, and make any necessary adjustments to their build systems to realize the full potential of Redux v5.0.0's modernized packaging. As the community adjusts, the collective experiences and findings will likely continue to shape best practices around ESM adoptability in Redux applications and beyond.

Codebase Modernization: Redux's TypeScript Overhaul and Best Practices

With Redux v5.0.0's transition to TypeScript, developers are thrust into a realm where type safety takes precedence, heralding an era of greater clarity and well-maintained code. TypeScript enforces strict type annotations, reducing runtime surprises and elevating the developer's ability to reason about state flow through the application.

The meticulous handling of types particularly shines through in middleware, where the nuanced typing of parameters allows for improved type safety. With the use of type guards, such as in the following updated middleware example, developers can ensure the integrity of action types:

// Correctly typed middleware with action type guard
import { Middleware, Dispatch } from 'redux';

interface KnownAction {
  type: string;
  // Additional expected properties

const typedLoggerMiddleware: Middleware<{}, any, Dispatch<KnownAction>> = store => next => action => {
  if (isKnownAction(action)) {
    console.log('Dispatching action:', action);
  return next(action);

function isKnownAction(action: any): action is KnownAction {
  return typeof action === 'object' && action !== null && 'type' in action;

TypeScript's union type literals employed as action types, complemented by Action and ActionCreator utility types, pave the way for cleaner and more explicit mappings of state and action correspondences. The example below showcases this best practice:

// Reducer using union type literals for better clarity and type safety
import { Action } from 'redux';

type TodoActions = 
  | Action<'TODO_ADD'> & { payload: { text: string; id: number } }
  | Action<'TODO_REMOVE'> & { payload: { id: number } };

function todoReducer(state: Todo[] = [], action: TodoActions): Todo[] {
  switch (action.type) {
    case 'TODO_ADD':
      return [...state, { text: action.payload.text, id: }];
    case 'TODO_REMOVE':
      return state.filter(todo => !==;
      return state;

The Redux Toolkit further eases TypeScript application by providing well-typed utilities such as configureStore, createAction, and createReducer. These tools facilitate a type-safe implementation that makes complex state logic both readable and maintainable:

// Utilizing Redux Toolkit's utilities for concise and typed Redux logic
import { createAction, createReducer, configureStore } from '@reduxjs/toolkit';

const addTodo = createAction<{ text: string; id: number }>('TODO_ADD');
const removeTodo = createAction<{ id: number }>('TODO_REMOVE');

const todosReducer = createReducer([], builder => {
  builder.addCase(addTodo, (state, action) => [...state, action.payload]);
  builder.addCase(removeTodo, (state, action) => state.filter(todo => !==;

const store = configureStore({
  reducer: { todos: todosReducer }

Adapting to v5.0.0, Redux encourages the use of UnknownAction to represent the state before type refinement takes place, as shown below:

// Embracing UnknownAction for proper type safety in Redux
import { UnknownAction, Reducer } from 'redux';

const initialState: unknown = [];

const refinedReducer: Reducer<unknown, UnknownAction> = (state = initialState, action) => {
  if (!Array.isArray(state)) {
    throw new Error('State must be an array for todosReducer');

  switch (action.type) {
    // Reducer cases...

function isTodoAction(action: unknown): action is TodoActions {
  return typeof action === 'object' && action !== null && 'type' in action;

Analyzing common pitfalls illustrates the criticality of type refinement, which steers clear of type assertion errors and sustains the reliability of applications. It is vitally important to enact runtime checks in parallel with static type assertions to preserve the sanctity of state. The enhanced example demonstrates how to adopt a consistent strategy for error handling in reducers:

// Improved error handling strategy with unknown types in reducers
function robustReducer(state: unknown, action: UnknownAction): Todo[] {
  if (!Array.isArray(state)) {
    throw new TypeError('Expected state to be an array in robustReducer');

  // Reducer logic using runtime type checks for action.type

By embracing TypeScript's strict type system and leveraging Redux's modern tooling, developers usher in a new age of state management excellence, characterized by improved type safety and heightened maintainability.

Refactoring Redux: Practical Code Transformations

As developers navigate the transition to Redux v5.0.0, refactoring Redux codebases is critical to align with the updated practices. One significant change involves moving away from the traditional createStore in favor of configureStore provided by Redux Toolkit. This change aims to simplify configuration, enhance middleware setup, and improve development experience.

// Prior Redux pattern using createStore
import { createStore, combineReducers } from 'redux';
import rootReducer from './reducers';

const store = createStore(
    // combine reducers here

// Updated practice using configureStore from Redux Toolkit
import { configureStore } from '@reduxjs/toolkit';
import rootReducer from './reducers';

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

In the example above, notice the inclusion of the devTools option directly within configureStore. This eliminates the manual integration previously done with createStore, hence streamlining the setup.

Another common transformation required with Redux v5.0.0 is the enforcement of string action types. Using anything other than string literals can cause type-related bugs and inconsistencies.

// Incorrect usage with non-string action type
const ADD_TODO = Symbol('ADD_TODO');

// Corrected usage with string action type
const ADD_TODO = 'ADD_TODO';

The above correction ensures that action types are consistent with Redux’s requirement for string literals, thus preventing potential confusion and errors in reducer functions.

Additionally, Redux v5.0.0 marks the createStore as deprecated, urging users to favor configureStore from Redux Toolkit for an improved setup. However, should you encounter legacy code that utilizes createStore, you can transition using an aliased import rename to avoid the deprecation warnings.

// Transitional approach using legacy_createStore to avoid deprecation warnings
// This is a temporary fix until the complete adoption of configureStore
import { legacy_createStore as createStore } from 'redux';

const store = createStore(rootReducer);

The code block above nods to a practical step for developers not yet ready to completely overhaul their state management setup, allowing for a smoother transition period.

Finally, refactoring involves adopting the builder callback pattern for createSlice, which replaces the earlier object map of reducers with a more fluid and expressive syntax.

// Outdated object map syntax for createSlice
import { createSlice } from '@reduxjs/toolkit';

const todoSlice = createSlice({
  name: 'todos',
  initialState: [],
  reducers: {
    todoAdded: (state, action) => {
      // reducer implementation

// Modern builder syntax using the builder callback
import { createSlice } from '@reduxjs/toolkit';

const todoSlice = createSlice({
  name: 'todos',
  initialState: [],
  reducers: {},
  extraReducers: (builder) => {
    builder.addCase('todoAdded', (state, action) => {
      // reducer implementation

More expressive and modifiable, the new builder callback pattern within createSlice yields a syntax that is easier to adapt and extend, beneficial for future maintenance and scaling.

Throughout the refactoring process, developers should be vigilant of common migration pitfalls, such as misplaced reducer logic or improper configuration setting. Always ensure action types are strings and leverage Redux Toolkit’s capabilities to abstract and streamline state management. With these nuanced updates to Redux coding standards, v5.0.0 sets the tone for a more cohesive and enhanced development workflow.

Embracing the Future: Adaptability and Long-term Considerations

As developers contemplate integrating Redux v5.0.0 into their projects, it is crucial to weigh the long-term benefits and costs. Transitioning to a new version of a core library isn't just about embracing the latest features; it's a strategic decision that requires understanding the inevitable direction of the web development ecosystem. What are the costs associated with updating an existing codebase versus the advantages of staying current with modern practices? Developers must assess not just the immediate impact of migration but also the extended benefits such as enhanced code safety and maintainability that TypeScript brings.

When planning for the future of an application, it is important to stay informed about the strategic shifts in design patterns heralded by a core library's updates. How will changes in common Redux patterns alter the approach to building scalable and maintainable systems? Proactively adapting to these evolving patterns allows developers to future-proof applications, making them more resilient to change and able to leverage the full power of Redux's capabilities.

Staying current with Redux means more than simply keeping up with its version numbers; it encompasses an understanding of and adaptation to the evolving JavaScript and React ecosystems. As tooling and language features evolve, state management patterns need to evolve as well. How will advances in the JavaScript language and updates in React affect Redux adoption and usage? Developers taking advantage of these changes might find more elegant solutions to state management, which could impact the relevance of Redux in their specific use cases.

Adaptability is key when considering not just the adoption of new Redux features but the broader technology landscape changes. The JavaScript ecosystem is dynamic, and methodologies can shift rapidly, thus how much should a development team invest in aligning its practices with these evolving patterns? The answer likely hinges on a combination of project needs, team skills, and the projected lifecycle of the application. Evaluating whether the short-term upheaval leads to long-term gains is essential in decision-making.

Encouragingly, while Redux evolves, it does so with a commitment to backward compatibility and incremental adoption. Still, it begs the question: In an ecosystem where new state management solutions are frequently introduced, what ensures Redux's long-term viability for your project? Weighing Redux's roadmap and its alignment with your project's trajectory is critical. This forward-thinking approach will not only manage the current state of your application efficiently but will also prepare it for the unforeseen advancements of tomorrow's development landscape.


The article explores the implications of dropping UMD builds in Redux v5.0.0, highlighting the shift from UMD to ESM/CJS formats, the benefits of the transition in terms of performance and bundle optimization, the codebase modernization with TypeScript and Redux Toolkit, and the importance of adaptability and long-term considerations. Key takeaways include the advantages of ESM/CJS modules, the impact on performance and bundle size, the use of TypeScript for type safety, practical code transformations for refactoring Redux codebases, and the need for developers to consider the future of state management and embrace evolving patterns. The challenging technical task presented to the reader is to evaluate the costs and benefits of updating an existing codebase to Redux v5.0.0, considering the advantages of staying current with modern practices and the potential impact of changes in common Redux patterns on building scalable and maintainable systems.

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