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React Compiler analyzes components and Hooks during the build and adds memoization where it can reuse work. It can reduce unnecessary renders and recalculations, but it is not a runtime speed switch or a guarantee that every app will become faster. For most new React 19 code, the recommended starting point is compiler integration plus profiling and tests—not adding useMemo, useCallback, and memo everywhere.
What React Compiler automatic memoization does
The compiler examines React components and Hooks at build time, then generates memoization so output or calculations can be reused when their inputs have not meaningfully changed. For example, if a parent updates for an unrelated reason, memoization may let a child avoid rendering again when the values it uses are unchanged. React describes this as an optimization, not a guarantee that React will never render a component. React Compiler documentation and the memo reference explain the behavior.
This is chiefly intended to improve update performance by avoiding unnecessary work. It does not memoize every JavaScript function: a standalone helper outside a component or Hook is not automatically memoized, and a cached calculation is not shared across separate components or Hooks. If an expensive helper runs in multiple places, profile the relevant workload before adding a separate cache or other complexity. The compiler introduction covers these limits.
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Install it in the build pipeline
Use the official setup guide for the build tool and project versions you actually have; package versions and integration details can change. The guide recommends installing babel-plugin-react-compiler as a development dependency. In a Babel configuration, put the compiler plugin first in the plugin list so it can analyze the original source before other transformations. The guide also documents Vite setup and directs React Native/Metro and other environments to their relevant instructions. See React Compiler installation.
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React version compatibility
React 19 is the preferred target, and most React 19 applications can use the default compiler configuration. React 17 and 18 are also supported, but require the react-compiler-runtime package and a target setting for the React version. Follow the current configuration reference rather than assuming a React 19 setup applies unchanged to an older project.
Enable compiler diagnostics
The installation guide recommends eslint-plugin-react-hooks to surface violations of React’s rules and code the compiler cannot optimize. A diagnostic does not necessarily block the whole build: the affected component or Hook can be skipped while eligible code elsewhere continues to compile. Treat lint feedback as a way to identify code to investigate, not as proof that every reported issue has the same cause or user impact.
Confirm that compilation is happening
React DevTools can show a “Memo ✨” badge on optimized components, and build output can contain compiler-generated memoization logic. These checks show that the compiler is operating; neither demonstrates a user-visible performance improvement. Measure the interaction or workload that matters in your application.
Choose a rollout scope that matches the project
A new or well-understood React 19 app can start with the standard integration and lint feedback. A larger or higher-risk codebase can adopt the compiler incrementally, limiting its initial scope and expanding after checking behavior and performance. The incremental adoption guide describes this approach.
| Approach | What it compiles | Useful when |
|---|---|---|
infer or all mode |
Functions selected by the compiler’s inference or broader compilation mode. | You want the compiler to handle eligible code without adding opt-in directives. Check the live configuration reference for the mode’s current behavior and options. |
annotation mode |
Functions that opt in with "use memo". |
You want a controlled, incremental rollout in selected functions or areas. |
"use no memo" |
Excludes the function where it appears; it can override a module-level opt-in. | You need a deliberate, documented exception while investigating behavior. |
Directives can appear at function level; a module-level directive can affect functions in that file. Configuration also includes target selection and other controls such as logging and error handling. Consult the directives reference and configuration reference for exact syntax and current options. Keep opt-outs intentional and record why they exist rather than using them to conceal an unresolved issue.
Keep manual memoization while you validate
For new code, React recommends relying on compiler memoization in most cases instead of routinely adding useMemo, useCallback, or memo. Those APIs remain available when you need more precise control—for example, stabilizing a value used as an Effect dependency. The compiler changes the default workflow; it does not make manual memoization invalid or universally unnecessary. React’s guidance explains the distinction.
In an existing app, leave current manual memoization in place initially. Remove it only after testing: changing or removing it can change what the compiler produces. Use profiling to compare the interactions that matter, and test behavior as well as render performance.
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React Compiler 1.0 was announced as stable on October 7, 2025. The React team described it as production-ready and reported using it on major apps at Meta; that characterization is not an independent benchmark or a promised speedup for another app. Read the React team’s 1.0 announcement.
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The team also cautions that JavaScript cannot always reveal statically when product code violates the Rules of React. A change in memoization can affect identity-sensitive behavior—for example, an Effect that depends on a value may run too often or too rarely if that value’s identity changes differently. Keep the code aligned with the Rules of React and use continuous end-to-end tests to catch behavior changes. Where test coverage is weak, the announcement recommends pinning the compiler to an exact version and upgrading deliberately.
For library authors, account for consumers’ React versions
A library supporting React versions below 19 has an additional packaging concern. The compiler’s library setup guide recommends declaring react-compiler-runtime as a direct dependency and configuring the minimum supported React target. Test the library both with and without compilation so its behavior does not depend on a consumer having the compiler enabled.
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