How to Migrate React UIs Without Breaking Everything

Migrating React UIs can feel like walking through a minefield—one wrong move and your entire app breaks. This guide shows developers and engineering teams exactly how to migrate React components and upgrade versions without destroying your production environment.

For a broader perspective on choosing the right frontend technology, check out our React vs Vue vs Angular comparison.

Who this is for: Frontend developers managing legacy React codebases, engineering teams planning major version upgrades, and anyone who's ever stared at a broken build, wondering what went wrong during a React migration.

You'll learn how to assess your current React setup to understand what you're working with before making any changes. If you’re also managing legacy Angular codebases, explore our detailed AngularJS to Angular migration guide. We'll cover choosing the right migration strategy for your specific project size and complexity—whether that's a gradual version-by-version approach or a more comprehensive overhaul. Finally, you'll discover how to execute safe version upgrades while handling breaking changes, managing dependencies, and testing everything along the way.

Stop letting React migration anxiety keep you stuck on outdated versions. With the right strategy, you can upgrade confidently and keep your app running smoothly.

Assess Your Current React Setup Before Migration

Check your current React version and dependencies

Before initiating any React migration, establishing a comprehensive inventory of your current setup is essential. Start by running npm list react or yarn list react to identify your exact React version. The React team specifically published version 18.3, which is functionally identical to 18.2 but emits warnings for any APIs that will break in React 19, making this assessment phase crucial for planning your migration strategy.

Document all your React-related dependencies, including React Router, state management libraries, UI frameworks, and any third-party components. Pay particular attention to packages that directly interact with React's core APIs, as these are most likely to encounter breaking changes during version upgrades. Create a dependency matrix that maps each package to its current version and React compatibility requirements.

Document existing functionality and performance baselines

Thorough documentation of your current application's functionality serves as your migration roadmap and success criteria. Catalog all existing React components, their props interfaces, state management patterns, and data flow architectures. This documentation becomes invaluable when troubleshooting migration issues or validating that functionality remains intact post-upgrade. Learn more about performance optimization techniques in our blog on frontend myths and best practices.

Establish performance baselines by measuring key metrics such as bundle size, initial load time, component render cycles, and memory usage. These metrics will help you quantify the impact of your React migration and ensure that performance improvements are actually achieved. Document any custom hooks, higher-order components, or render props patterns, as these may require special attention during migration to newer React paradigms.

Ensure comprehensive test coverage for easier troubleshooting

Comprehensive test coverage acts as your safety net during React migration, catching breaking changes before they reach production. Focus on unit tests for individual components, integration tests for component interactions, and end-to-end tests for critical user workflows. The reference content emphasizes that proper testing is necessary to find bugs, compatibility issues, and performance problems that emerge during migration.

Prioritize testing components that handle complex state management, asynchronous operations, or integrate with external APIs. These areas are most susceptible to breaking changes when upgrading React versions. Ensure your test suite covers edge cases and error scenarios, as React 19's improved Suspense behavior and new Actions API may change how these situations are handled.

Create a complete backup with version control commits

Before proceeding with any React migration work, create a clean, tagged commit in your version control system that represents your current stable state. This backup serves as your rollback point if migration issues prove too complex to resolve quickly. The migration process should follow a phased approach where each significant change is committed separately, allowing for granular rollbacks if needed.

Use descriptive commit messages that clearly indicate migration-related changes, making it easier to track progress and identify problematic commits. Consider creating a dedicated migration branch where you can safely experiment with changes before merging to your main development branch. This approach aligns with the best practice of using version control systems like Git for maintaining team collaboration during complex migration projects.

Choose the Right Migration Strategy for Your Project

Evaluate gradual version-by-version upgrades vs direct jumps

When planning your React migration strategy, the choice between incremental version updates and direct jumps to the latest version significantly impacts project success. Gradual version-by-version upgrades offer the safest path forward, allowing developers to address breaking changes systematically and test each increment thoroughly.

The incremental approach minimizes risk by distributing the migration workload over time. Each version upgrade brings manageable changes that can be addressed individually, reducing the likelihood of introducing critical bugs. This method proves especially valuable for production applications where stability cannot be compromised.

Conversely, direct jumps to the latest React version can accelerate the migration timeline but introduce substantial complexity. Multiple breaking changes must be resolved simultaneously, potentially overwhelming development teams and creating cascading issues throughout the codebase.

For most projects, the gradual approach provides better control and visibility into potential problems. Teams can measure performance impacts after each version increment, ensuring that improvements align with migration goals before proceeding to the next stage.

Consider component-by-component migration for large applications

Component-by-component migration represents the most practical strategy for large-scale React applications. This approach aligns perfectly with React's fundamental design philosophy of creating reusable, self-contained components that can coexist with existing solutions.

The beauty of this strategy lies in React's ability to work alongside legacy systems without requiring complete application rewrites. You can identify small, isolated components as initial migration candidates - perhaps a simple button, modal, or list component - and gradually expand your React footprint.

Start by selecting components with minimal dependencies and straightforward functionality. These serve as proof-of-concepts that demonstrate React's integration capabilities while building team confidence. As the reference content emphasizes, you don't need to migrate the whole app at once, making this approach particularly attractive for risk-averse organizations.

This incremental method allows for A/B testing between legacy and React components, providing valuable data on conversion rates and user experience improvements. Teams can measure the impact of each migrated component against key performance indicators established before migration begins.

Assess the microfrontend approach for complex legacy systems

For organizations managing complex legacy systems, the microfrontend approach offers a sophisticated migration strategy that maintains architectural independence while enabling gradual modernization. This strategy becomes particularly relevant when dealing with deprecated frameworks or monolithic applications that resist traditional migration approaches.

Microfrontends allow different teams to work independently on separate application sections, each potentially using different React versions or even different frameworks entirely. This approach provides maximum flexibility for organizations with diverse technical requirements and varying migration timelines.

The strategy proves especially valuable when migrating from frameworks like AngularJS, where the architectural differences create significant integration challenges. By treating each application section as an independent microfrontend, teams can migrate at their own pace without blocking other development efforts.

However, this approach requires careful consideration of shared dependencies, routing strategies, and inter-application communication patterns. Teams must establish clear boundaries and communication protocols to prevent conflicts between different frontend implementations.

Plan for a monorepo structure with shared design systems

Monorepo structures combined with shared design systems provide an elegant solution for maintaining consistency during large-scale React migrations. This approach ensures that migrated components maintain visual and functional consistency with existing application elements.

The monorepo structure enables centralized management of shared React components, utilities, and design tokens. Teams can create a component library that serves both legacy and new React implementations, gradually expanding the shared component ecosystem as migration progresses.

Shared design systems become particularly crucial when implementing component-by-component migrations. They ensure that new React components seamlessly integrate with existing UI elements, preventing the jarring visual inconsistencies that can occur during gradual migrations.

This strategy also facilitates better collaboration between design and development teams, as shared components serve as a single source of truth for UI patterns. The approach supports the incremental migration philosophy by allowing teams to replace legacy components with their React equivalents systematically, maintaining design consistency throughout the process.

The monorepo structure simplifies dependency management across different application sections, ensuring that all teams use compatible versions of shared libraries and design system components.

Execute Safe Version Upgrades

Use official React upgrade guides and migration tools

React's official upgrade documentation provides comprehensive guidance for each version transition, particularly for major releases like React 19. The React team publishes detailed upgrade guides that outline breaking changes, new features, and migration steps. For React 19 specifically, the upgrade process involves installing the latest version using npm install --save-exact react@^19.0.0 react-dom@^19.0.0 or the equivalent Yarn command.

The React team has partnered with codemod.com to provide automated migration tools through the react-codemod repository. These codemods automatically update your code to new APIs and patterns. Rather than using the legacy react-codemod command, it's recommended to use the newer codemod command, which runs faster, handles complex code migrations more effectively, and provides better TypeScript support.

Key codemods available for React 19 migration include:

• npx codemod@latest react/prop-types-typescript for converting PropTypes to TypeScript

• npx codemod@latest react/19/replace-string-ref for updating string refs to callback refs

• npx codemod@latest react/19/replace-reactdom-render for migrating from ReactDOM.render to createRoot

• npx types-react-codemod@latest preset-19 ./path-to-app for TypeScript-related changes

Start with separate branches for isolated testing

Before implementing any React version upgrade in your main codebase, create dedicated feature branches for migration work. This approach allows you to isolate potential issues and test changes without affecting your production environment. Create a branch specifically for the React upgrade using git checkout -b feature/react-19-migration and conduct all migration activities within this isolated environment.

Working in separate branches enables you to:

• Test the migration incrementally without disrupting ongoing development

• Compare the before and after states easily

• Roll back changes quickly if critical issues arise

• Share migration progress with team members for review

• Run automated tests against the migrated code before merging

This isolation strategy is particularly crucial when dealing with breaking changes in React 19, such as the removal of deprecated APIs like propTypes, defaultProps for function components, legacy Context APIs, and string refs. Each of these changes can potentially break existing functionality, making branch isolation essential for safe migration.

Follow React Native Upgrade Helper for mobile applications

For React Native projects, the React Native Upgrade Helper (rn-diff-purge) provides version-specific migration guidance. This tool shows exact differences between React Native versions, helping you understand what files need modification during the upgrade process. The helper generates comprehensive diffs that highlight changes in configuration files, native dependencies, and React Native-specific APIs.

When upgrading React Native applications, consider these additional factors:

• Native module compatibility with the new React version

• Platform-specific breaking changes for iOS and Android

• Metro bundler configuration updates

• Gradle and CocoaPods dependency modifications

The upgrade process for React Native typically involves more complex considerations than web-only React applications, as you must account for native platform dependencies and potential breaking changes in the React Native framework itself.

Address breaking changes systematically before proceeding

React 19 introduces several breaking changes that require systematic resolution before completing the migration. The most significant changes include the removal of deprecated APIs such as PropTypes and defaultProps for function components, legacy Context using contextTypes and getChildContext, string refs, module pattern factories, and React.createFactory.

Error handling behavior has also changed in React 19. Previously, errors thrown during render were caught and rethrown, but now uncaught errors are reported to window.reportError while caught errors go to console.error. This change may impact production error reporting systems that rely on errors being re-thrown.

Additional breaking changes include:

• Removal of ReactDOM.render in favor of createRoot

• Elimination of ReactDOM.hydrate for hydrateRoot

• Deprecation of react-test-renderer with recommendations to use modern testing libraries

• TypeScript type changes requiring useRef to accept arguments

• JSX namespace modifications requiring module augmentation updates

Address each breaking change methodically by running the appropriate codemods, updating deprecated API usage, and testing functionality after each modification. This systematic approach ensures that no critical issues are overlooked during the migration process.

Handle Breaking Changes and Dependencies

Update incompatible third-party libraries and packages

Now that we have covered choosing the right migration strategy, it's crucial to address library compatibility issues that can derail your React migration. React 19 introduces several breaking changes that affect how third-party packages interact with your application.

Start by auditing your package.json dependencies using automated tools or manual inspection. Libraries that depend on deprecated React APIs like ReactDOM.render, ReactDOM.hydrate, or ReactDOM.unmountComponentAtNode will require immediate attention. These APIs have been completely removed in React 19, forcing you to update to versions that support ReactDOM.createRoot and ReactDOM.hydrateRoot.

Pay special attention to testing libraries, as many depend on React internals. The react-test-renderer/shallow package has been removed, requiring migration to react-shallow-renderer as a direct dependency. Additionally, ReactDOMTestUtils.act has moved from react-dom/test-utils to the main react package, necessitating import updates across your test files.

UI component libraries often lag behind React releases. Before upgrading, verify that your chosen libraries (Material-UI, Ant Design, Chakra UI) have released compatible versions. Some may require significant version jumps or alternative implementations.

Create a dependency compatibility matrix to track which packages need updates, which have breaking changes, and which require complete replacement. This systematic approach prevents runtime errors and ensures your migration proceeds smoothly without unexpected package conflicts.

Migrate from class components to functional components with hooks

With dependency updates addressed, migrating class components to functional components represents one of the most impactful changes for React migration success. React 19's performance optimizations, particularly the React Compiler, work more effectively with functional components and hooks.

Begin by identifying class components that use deprecated patterns. String refs, which were deprecated in March 2018, must be converted to ref callbacks or the useRef hook. Legacy Context using contextTypes and getChildContext requires migration to the modern Context API with createContext and useContext.

// Before: Class component with string refs
class MyComponent extends React.Component {
  componentDidMount() {
    this.refs.input.focus();
  }
  render() {
    return <input ref='input' />;
  }
}

// After: Functional component with useRef
function MyComponent() {
  const inputRef = useRef(null);
  useEffect(() => {
    inputRef.current.focus();
  }, []);
  return <input ref={inputRef} />

Focus on components using deprecated lifecycle methods. componentWillMount, componentWillReceiveProps, and componentWillUpdate have safer alternatives using hooks like useEffect, useMemo, and useCallback. This migration improves component predictability and aligns with React's concurrent rendering capabilities.

Leverage React's provided codemods to automate much of this conversion process. The react-codemod repository offers transformations for string refs, propTypes removal, and other common migration patterns, significantly reducing manual effort while maintaining code consistency.

Address deprecated APIs and lifecycle methods

Previously, we've covered component migration strategies, but addressing deprecated APIs requires systematic identification and replacement of outdated React patterns. React 19 removes several long-deprecated APIs that may still exist in legacy codebases.

The removal of propTypes and defaultProps for functional components, marks a significant shift toward TypeScript or other type-checking solutions. Instead of runtime prop validation, React 19 encourages compile-time type checking using ES6 default parameters for functional components.

// Before: PropTypes and defaultProps
function Heading({text}) {
  return <h1>{text}</h1>;
}
Heading.propTypes = {
  text: PropTypes.string,
};
Heading.defaultProps = {
  text: 'Hello, world!',
};

// After: TypeScript with default parameters
interface Props {
  text?: string;
}
function Heading({text = 'Hello, world!'}: Props) {
  return <h1>{text}</h1>

Legacy Context APIs using contextTypes and getChildContext must transition to the modern Context API. This change eliminates subtle bugs while improving component composition and data flow predictability. The migration involves creating context objects with createContext and consuming them through useContext hooks or contextType for class components.

Module pattern factories, rarely used but still supported in older React versions, no longer function in React 19. These patterns required components to return objects with render methods rather than JSX directly, creating unnecessary complexity and performance overhead.

Use the available codemods to automate these transformations: npx codemod@latest react/prop-types-typescript for propTypes migration and npx codemod@latest react/19/replace-string-ref for string ref updates.

Ensure Node.js version compatibility throughout the process

With deprecated APIs addressed, maintaining Node.js version compatibility becomes critical for successful React migration. React 19 requires specific Node.js versions to function properly, and mismatched versions can cause cryptic build failures or runtime errors.

Verify that your development and production environments meet React 19's Node.js requirements. Update your .nvmrc file to specify the required Node version, ensuring team consistency across different development machines. CI/CD pipelines must also target compatible Node versions to prevent deployment failures.

Package managers like npm and Yarn have version-specific behaviors that can affect dependency resolution. React 19's package structure changes may expose incompatibilities with older package manager versions. Upgrade to recent npm (8.0+) or Yarn (3.0+) versions to ensure proper dependency handling.

Build tools and bundlers often depend on specific Node.js features. Webpack, Vite, and other bundling solutions may require updates to support React 19's new JSX transform requirements. Test your build process thoroughly after Node.js updates to identify configuration changes needed for successful compilation.

Document Node.js version requirements in your project README and deployment guides. Include specific version numbers rather than ranges to prevent subtle compatibility issues that emerge over time. This documentation helps new team members and deployment engineers maintain consistent environments throughout the React migration process.

Test and Validate Migration Success

Run comprehensive testing in QA environments

Now that we have covered the execution of migration steps, the validation phase becomes critical for ensuring React migration success. Building a robust testing pipeline requires implementing a systematic approach that can handle large-scale migrations efficiently. Based on proven migration strategies, comprehensive testing should follow a step-based validation process where each file moves through stages of verification.

The most effective approach involves creating a state machine-like flow for your React migration testing. Each component or file should progress through discrete validation stages, moving to the next state only after the previous validation passes. This methodical approach enables you to track progress across thousands of files while maintaining quality standards throughout the migration process.

For large-scale React UI migrations, implementing automated validation steps proves essential. Your QA environment should include checks for Jest compatibility, ESLint compliance, TypeScript compilation, and overall functionality. This stepped approach provides a solid foundation for automation and makes it simple to run migrations on hundreds of files concurrently, which is critical for both quickly validating simple components and systematically addressing complex cases.

Monitor application performance after each upgrade step

With comprehensive testing in place, performance monitoring becomes your next critical validation layer. Performance tracking should occur at each migration step to identify potential regressions before they compound into larger issues. Implement monitoring that captures key metrics like component render times, bundle sizes, and overall application responsiveness.

The step-based validation approach allows for granular performance tracking, where you can isolate performance impacts to specific migration phases. This systematic monitoring helps identify when particular React version upgrades or dependency changes introduce performance bottlenecks, enabling quick rollback decisions when necessary.

Establish baseline performance metrics before beginning your migration and compare against these benchmarks after each validation step. This data-driven approach ensures that your React migration maintains or improves application performance rather than introducing unexpected slowdowns.

Fix bugs incrementally before moving to the next version

Previously established validation steps enable incremental bug fixing that prevents issues from accumulating throughout the migration process. When validation failures occur, implement retry loops with dynamic prompting to address issues systematically. This approach allows you to resolve simple-to-medium complexity issues efficiently while identifying files that require more intensive attention.

For React migration testing, the most effective strategy involves implementing configurable retry mechanisms where failing components can be reprocessed multiple times until they pass validation or reach predetermined limits. This brute force approach, combined with dynamic error feedback, successfully resolves a large percentage of migration issues without manual intervention.

Track common failure patterns across your migration to identify systematic issues that can be addressed through improved validation scripts or enhanced migration tooling. This breadth-first approach to bug fixing ensures you address the most common issues across your codebase rather than getting stuck on edge cases.

Deploy to production only after thorough validation

The final validation phase requires achieving high success rates across your entire migration scope before considering production deployment. Based on successful large-scale migrations, aim for at least 95-97% automated success rates before manual intervention becomes necessary. This threshold ensures that the vast majority of your React components have been thoroughly validated and tested.

Implement a systematic improvement process for addressing remaining validation failures. Use a "sample, tune, sweep" methodology where you identify common issues affecting multiple files, update your validation criteria to address these patterns, and then re-run validation across all remaining components. This approach efficiently tackles the long tail of complex migration cases.

For the small percentage of files that don't complete through automated validation, your testing pipeline should provide solid baselines for manual review. This hybrid approach - combining automated validation with targeted manual intervention - ensures complete migration coverage while maintaining efficiency and quality standards essential for safe production deployment.

Maintain Consistency During Large-Scale Migrations

Extract reusable UI components into shared design systems

Now that we have covered the technical aspects of React migration, maintaining consistency during large-scale migrations requires establishing reusable UI components within shared design systems. This approach becomes particularly crucial when migrating React UIs across multiple teams and features simultaneously. Check out our comprehensive guide on mastering UI libraries in 2025 for advanced insights.

Design systems serve as the foundation for consistency by providing a centralized collection of components like buttons, modal dialogs, layouts, and tooltips that can be used throughout your application. When implementing a migration strategy, these components should be extracted into dedicated packages within a monorepo architecture, making them accessible across all features through clear naming conventions like @project/button or @project/modal.

The key advantage of this approach lies in aliasing - rather than using relative imports like import { Button } from '../../../components/button', teams can reference components by name: import { Button } from '@project/button'. This creates instant clarity about what components are part of your design system versus feature-specific implementations.

Migrate one route or feature at a time for manageable changes

Breaking down large-scale React migrations into manageable chunks requires adopting a feature-by-feature migration approach. This strategy aligns with the decomposition principle where your React project is viewed as a composition of independent features rather than a monolithic application.

Each feature should be treated as an isolated "nanoservice" that communicates with other features through external APIs (typically React props). This isolation enables teams to work independently on different features in parallel, reducing conflicts and allowing for more controlled migration rollouts.

The monorepo package structure supports this approach perfectly. Features extracted into packages like @project/settings, @project/user-profile, or @project/dashboard can be migrated individually while maintaining their public API contracts. When refactoring the internals of a feature package, other parts of the application remain unaffected as long as the external interface stays consistent.

Preserve visual consistency across old and new implementations

Maintaining visual consistency during migration requires careful planning to ensure users don't experience jarring interface changes as features are updated. The hierarchical structure within packages plays a crucial role in achieving this consistency.

Within each feature package, establishing clear layers - particularly the "shared" layer for common UI components and the "ui" layer for feature-specific implementations - ensures consistent visual patterns. Components that need to be shared between different levels of the hierarchy should be extracted to the shared layer, preventing visual inconsistencies that arise from duplicated styling or behavior.

The strict hierarchy principle prevents components from importing from "neighbors" or "parents," forcing teams to think carefully about shared visual elements. When a component needs to be used across different parts of the application, it naturally gets promoted to the appropriate shared layer, ensuring consistency.

Plan for final cleanup and consolidation of migrated code

The final phase of large-scale React migration involves systematic cleanup and consolidation of migrated code. This process benefits significantly from the package-based architecture's refactoring advantages.

With features properly separated into packages, cleanup becomes straightforward. Components that are no longer needed can be removed without affecting other parts of the system, since package boundaries prevent unexpected dependencies. The clear separation of concerns between layers (data, shared, and UI) makes it easy to identify obsolete code and remove it safely.

Refactoring during cleanup is particularly seamless with this architecture. Since packages are referenced by name rather than location, you can reorganize the physical structure by dragging and dropping folders without breaking imports. Renaming packages requires only a simple search and replace operation across the project.

The package approach also supports gradual consolidation - similar features can be merged by combining their packages and updating import statements, while the rest of the application continues functioning normally. This flexibility ensures that the cleanup phase doesn't introduce new instability after a successful migration.

Conclusion

React UI migrations don't have to be a source of anxiety when approached systematically. By thoroughly assessing your current setup, choosing the right migration strategy, and executing safe version upgrades while carefully handling breaking changes, you can navigate even complex migrations successfully. The key is maintaining rigorous testing throughout the process and ensuring consistency across your entire application during large-scale changes. For strategies on modernizing legacy applications, see our Ultimate Guide to Enterprise App Modernization.

Remember that staying current with React versions brings significant benefits, including performance improvements, security patches, and access to new developer tooling. Whether you're upgrading gradually, version by version, or implementing a more comprehensive migration strategy, the investment in proper planning and execution will pay dividends in the long run. Take the time to commit your changes, test thoroughly, and don't rush the process—your future self and your users will thank you for the careful approach.