The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →React.memo can help React skip rendering a functional component when its props have not changed. Use it selectively: profile a real interaction first, then memoize a component that often receives the same props and does enough rendering work for skipping it to matter. It is an optimization, not a fix for incorrect behavior or a guarantee that a component will never render.
When React.memo is worth using
React’s memo(Component, arePropsEqual?) returns a memoized component. When its parent renders again, React will usually skip rendering the memoized child if its props are unchanged. Its own state changes and changes to context it uses can still cause it to render.
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The useful case is specific: the child renders frequently, usually receives the same props, and its rendering work is costly enough that avoiding it improves a real interaction. If you do not notice lag, React says memoization is unnecessary. Start with the React memo guidance and use the React Developer Tools Profiler to identify which components actually benefit.
Start with a measured interaction
- Reproduce the interaction that feels slow, such as typing into a field or changing a filter.
- Record it with the React Developer Tools Profiler and look for children that render repeatedly while their relevant inputs remain unchanged.
- Consider
memofor a child only if avoiding its render is likely to reduce the measured work or improve the interaction. - Profile the same interaction after the change. Keep the memoization only if it provides a practical benefit.
How to memoize a functional component
Import memo, wrap the component, and use the returned component in place of the original:
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import { memo } from 'react';
const Profile = memo(function Profile({ name, age }) {
return <section>{name}: {age}</section>;
});Wrapping a component does not automatically make it faster. Its props must be able to remain equal between parent renders, and the work it would otherwise do must be worth skipping.
Why object, array, and function props can defeat memo
By default, React compares each prop with Object.is. If a parent creates an object, array, or function during every render, the new value has a different identity—even when its contents or behavior appear unchanged. The memoized child can therefore render again.
Pass only the values the child needs
Before stabilizing a prop, consider whether the child needs the whole object. Passing the specific values it uses is often simpler:
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<Profile name={user.name} age={user.age} />Stabilize a necessary object or callback
If the child needs an object value, useMemo can preserve its reference until its dependencies change. If it needs a callback, declare the function outside the parent component when possible, or use useCallback when the function depends on values from the parent. These hooks are useful when stable identity supports a real optimization, not as automatic additions to every prop. See React’s guidance for useMemo and useCallback.
When to use a custom comparison
The optional arePropsEqual comparator is a rare escape hatch, not the first response to a child that keeps rendering. A custom comparator must account for every prop, including functions. If it returns true when a callback has changed, the child may keep using a callback that closes over outdated values.
Comparing nested data can also cost more than rendering the component, particularly if the data grows. Consider a custom comparator only after profiling shows the default prop comparison is insufficient. Check every prop, ensure the result means the component would behave identically, and measure the comparator’s cost against rendering in production mode. Avoid unbounded deep comparisons.
What React.memo does not fix
Do not add memoization to fix visual glitches, side effects, or incorrect output. React components should render purely from their inputs. Fix impure rendering and unnecessary effect-driven updates first; keep transient state close to where it is used instead of lifting it higher than necessary. React’s guidance is to rely on memo only for performance: if the code does not work without it, fix the underlying problem before optimizing.
Do you still need React.memo with React Compiler?
When React Compiler is enabled, it typically optimizes component rendering automatically, so manual React.memo is usually unnecessary. Check whether the compiler is enabled in your project before adding manual memoization; follow the React Compiler introduction for its behavior and setup context. If it is not enabled, use manual memoization only for measured hot paths rather than applying it everywhere.
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