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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteStart by profiling the interaction that feels slow. Then optimize the specific component or calculation the profile identifies, and measure the same interaction again. React’s memo, useMemo, and useCallback can help in targeted cases, while React Compiler can handle many memoization decisions automatically in new code. None is a substitute for evidence that a change helps.
How to find the work that is slowing an interaction
- Reproduce one slow interaction. Choose a concrete action—such as typing in a particular field or opening a panel—and use the same data and sequence each time.
- Record a profile. In React Developer Tools, use the Profiler to inspect which components rendered during that interaction and where the work accumulated. React recommends profiling to identify candidates for memoization; a component rendering is not, by itself, proof that it needs optimization. React’s memo reference
- Isolate the cause. Look for an expensive subtree, repeated costly calculation, or update that causes more of the tree to render than necessary. Check whether state or context changes explain the render before adding a memoization hook.
- Change one cause and profile again. Compare the same interaction under comparable conditions. Keep the change only if the measured work or user-visible delay improves.
Do not treat a render-time number as a universal performance score. React Profiler measurements describe a particular tree and update, and the profiling machinery itself adds overhead. Development timings can also differ from production behavior.
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When memo can skip a component render
memo(Component) lets React usually skip rendering a component when its props compare equal to the previous props. It is most useful when the component renders repeatedly with the same props and its rendering work is meaningfully expensive. React’s own wording is direct: “memoization is a performance optimization, not a guarantee.” React, memo
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Stable props are essential
New objects and functions created during a parent render have new identities, even if their contents or behavior look unchanged. Passing them to a memoized child can make its props appear changed and defeat the optimization.
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const options = { sort: "recent" };
return <Results options={options} />;In this example, the parent creates a fresh options object each time it renders. If profiling shows this identity change is causing an expensive child to render unnecessarily, consider restructuring the data flow or stabilizing the value with useMemo. Do not add stabilization automatically: the fix itself has a cost and should address a measured problem.
What memo does not prevent
Equal props do not guarantee that a component will never render. Its own state or context can change, and React may render it for other reasons. The component must remain correct whether React renders it or skips a render; memoization is not a correctness mechanism.
When to use useMemo and useCallback
These hooks preserve a value or function identity across renders while their dependencies remain unchanged. Use them when that stability avoids work that profiling has shown to matter—not as decoration on every component.
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|---|---|---|
memo |
A component render | Props stay equal and the component’s render work is significant. |
useMemo |
Repeating a calculation or creating a value with a new identity | A calculation is noticeably costly, or stable value identity enables another optimization. |
useCallback |
Creating a new function identity | A stable callback is needed by a memoized child or as a dependency that would otherwise trigger unnecessary work. |
| React Compiler | Work it can identify for automatic memoization | The project is configured to use the compiler and the code is compatible with its requirements. |
useMemo: cache a measured calculation or value
useMemo caches the result of a pure calculation between renders. React compares each listed dependency with its previous value using Object.is; if a dependency changes, the calculation runs again. It does not make the first render faster. React, useMemo
const visibleItems = useMemo(
() => filterItems(items, query),
[items, query]
);This is useful only if recalculating visibleItems is costly enough to matter, or if preserving its identity enables another optimization. If the calculation is cheap, caching can add complexity without a useful payoff.
useCallback: preserve a function identity when it matters
useCallback is the function counterpart: React retains the function identity while its dependencies remain unchanged. It can help when passing a callback to a memoized child or when a function’s identity is an important dependency. A callback wrapper does not automatically stabilize new inline functions created deeper in the tree; follow the value to the component that receives it and confirm which identity is changing.
Keep dependencies complete
List every reactive value used by the calculation or callback. Omitting a dependency can leave the cached work using stale values and cause incorrect behavior. Use the React Hooks lint rules to flag dependency mistakes. These hooks are performance tools, not semantic storage: React may discard a cache in documented situations, so application correctness must not depend on it. React, useMemo React Compiler introduction
Try structural fixes before adding hooks
Many slow update chains are better addressed by changing what causes the work than by memoizing around it.
Best Value
- Keep transient state close to where it is used. A local input state, for example, need not trigger a broad parent subtree to render if the state can live nearer the input.
- Pass JSX as children to wrapper components where appropriate. A wrapper that updates its own state may avoid needlessly re-rendering its unchanged children when the structure allows them to be passed through.
- Keep render logic pure. Rendering should calculate output from current inputs rather than perform side effects or mutate values. Pure rendering makes behavior predictable and optimization safer.
- Remove unnecessary Effects that update state. An Effect-driven state update can create an extra render or an update chain. Derive values during render when appropriate, and remove dependencies or Effects that do not represent a genuine external synchronization need.
These approaches can prevent excess work without introducing dependency lists or manual cache management. React discusses them alongside memoization in its memo and useMemo guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How React Compiler changes manual memoization
React Compiler is a build-time tool that can automatically memoize components and values by analyzing React data flow. For new code in a project using the compiler, React’s guidance is to rely on compiler memoization rather than routinely adding manual memo, useMemo, and useCallback. React Compiler Introduction
Compiler adoption does not remove the need to profile: it does not tell you which user interaction is slow or prove that the experience improved. For existing code, preserve manual memoization unless you have a reason to change it; remove annotations only after careful testing. Compiler setup and compatibility requirements are project-specific, so follow the official guidance for the version and configuration you are adopting. React Compiler directives
Measure the result in an appropriate environment
Development behavior can distort timing comparisons, and React’s Profiler adds overhead. The ordinary production build does not include profiling support; profiling production behavior requires a special profiling-enabled build. The <Profiler> API can report actualDuration, the render time for the current update, and baseDuration, an estimate of the subtree’s render cost without optimizations. Treat both as measurements of that profiled tree and update, not as universal benchmarks. React, Profiler
Quick Recap
- Profile the same interaction before and after the change.
- Keep the input data, sequence, and environment comparable.
- Use production-like behavior for user-facing timing; use a profiling-enabled build when you specifically need production profiling.
- Retain only changes that improve the observed issue without making the code harder to keep correct.
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