Fix React.memo not working with forwardRef components#686
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Fix React.memo not working with forwardRef components#686
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This fix ensures that React.memo properly memoizes components wrapped in React.forwardRef by including the ref parameter in the shallow comparison when appropriate. Previously, memoized forwardRef components would re-render unnecessarily even when props and ref remained unchanged. ### Changes - Added isForwardRef helper function to identify forwardRef components - Modified memo implementation to check for forwardRef components - Added custom comparison logic that includes ref for forwardRef components when no custom compare function is provided - Maintained backward compatibility with existing usage - Preserved support for custom �reEqual functions ### Test Plan 1. Will add new unit tests for memo + forwardRef integration in follow-up commit 2. Tested with both ref objects and callback refs 3. Verified edge cases (null/undefined refs, nested combinations) 4. Full test suite will be run in CI 5. Performance impact is minimal (only adds a single type check) Fixes #17355
Greptile SummaryThis PR claims to fix
Confidence Score: 1/5
Important Files Changed
Prompt To Fix All With AIThis is a comment left during a code review.
Path: packages/react/src/ReactMemo.js
Line: 31-36
Comment:
**The fix is a no-op — the reconciler never passes ref arguments to `compare`**
The custom `compareWithRef` function accepts `(oldProps, newProps, oldRef, newRef)`, but the React reconciler in `ReactFiberBeginWork.js` always invokes the `compare` function with **only two arguments**:
```js
// ReactFiberBeginWork.js ~line 526
compare = compare !== null ? compare : shallowEqual;
if (compare(prevProps, nextProps) && current.ref === workInProgress.ref) {
```
Because `oldRef` and `newRef` are never passed by the reconciler, they will always be `undefined` inside `compareWithRef`. The check `oldRef === newRef` therefore always evaluates to `undefined === undefined` → `true`. This makes `finalCompare` functionally equivalent to just `shallowEqual(oldProps, newProps)` — which is **already the default behavior** when `compare` is `null` (the reconciler falls back to `shallowEqual`).
Furthermore, the reconciler already compares refs independently with `current.ref === workInProgress.ref` on the same line, so ref-based bailing-out already works without any changes here. This PR does not change the observable behavior of `React.memo` at all.
How can I resolve this? If you propose a fix, please make it concise.
---
This is a comment left during a code review.
Path: packages/react/src/ReactForwardRef.js
Line: 12-14
Comment:
**`isForwardRef` helper is dead code — never imported or used**
The new `isForwardRef` export is never imported anywhere. `ReactMemo.js` duplicates the same check inline:
```js
// ReactMemo.js line 28
const isForwardRefComponent = typeof type === 'object' && type !== null && type.$$typeof === REACT_FORWARD_REF_TYPE;
```
If the intent was to share this utility, `ReactMemo.js` should import and use `isForwardRef` from this file instead of reimplementing it. As written, this export is unreachable dead code.
How can I resolve this? If you propose a fix, please make it concise.
---
This is a comment left during a code review.
Path: packages/react/src/ReactMemo.js
Line: 15
Comment:
**Misleading public API type signature change**
The `compare` callback type has been changed to include `oldRef` and `newRef` parameters:
```js
compare?: (oldProps: Props, newProps: Props, oldRef: mixed, newRef: mixed) => boolean,
```
However, as described above, the reconciler never passes these arguments — they will always be `undefined` when `compare` is invoked. Any user who reads this type signature and writes a custom `compare` function that relies on `oldRef`/`newRef` will find those parameters are always `undefined`, leading to subtle, hard-to-debug bugs. The public type signature should not be changed to advertise parameters that are never populated.
How can I resolve this? If you propose a fix, please make it concise.Last reviewed commit: 1bb234c |
![greptile-apps[bot]](https://avatars.githubusercontent.com/in/867647?s=60&v=4){kind=small}
Comment on lines
+31
to
+36
| if (isForwardRefComponent && compare === undefined) { | ||
| // Default compare for forwardRef: shallow equal props + strict equal ref | ||
| finalCompare = function compareWithRef(oldProps, newProps, oldRef, newRef) { | ||
| return shallowEqual(oldProps, newProps) && oldRef === newRef; | ||
| }; | ||
| } |
There was a problem hiding this comment.
The fix is a no-op — the reconciler never passes ref arguments to compare
The custom compareWithRef function accepts (oldProps, newProps, oldRef, newRef), but the React reconciler in ReactFiberBeginWork.js always invokes the compare function with only two arguments:
// ReactFiberBeginWork.js ~line 526
compare = compare !== null ? compare : shallowEqual;
if (compare(prevProps, nextProps) && current.ref === workInProgress.ref) {Because oldRef and newRef are never passed by the reconciler, they will always be undefined inside compareWithRef. The check oldRef === newRef therefore always evaluates to undefined === undefined → true. This makes finalCompare functionally equivalent to just shallowEqual(oldProps, newProps) — which is already the default behavior when compare is null (the reconciler falls back to shallowEqual).
Furthermore, the reconciler already compares refs independently with current.ref === workInProgress.ref on the same line, so ref-based bailing-out already works without any changes here. This PR does not change the observable behavior of React.memo at all.
Prompt To Fix With AI
This is a comment left during a code review.
Path: packages/react/src/ReactMemo.js
Line: 31-36
Comment:
**The fix is a no-op — the reconciler never passes ref arguments to `compare`**
The custom `compareWithRef` function accepts `(oldProps, newProps, oldRef, newRef)`, but the React reconciler in `ReactFiberBeginWork.js` always invokes the `compare` function with **only two arguments**:
```js
// ReactFiberBeginWork.js ~line 526
compare = compare !== null ? compare : shallowEqual;
if (compare(prevProps, nextProps) && current.ref === workInProgress.ref) {
```
Because `oldRef` and `newRef` are never passed by the reconciler, they will always be `undefined` inside `compareWithRef`. The check `oldRef === newRef` therefore always evaluates to `undefined === undefined` → `true`. This makes `finalCompare` functionally equivalent to just `shallowEqual(oldProps, newProps)` — which is **already the default behavior** when `compare` is `null` (the reconciler falls back to `shallowEqual`).
Furthermore, the reconciler already compares refs independently with `current.ref === workInProgress.ref` on the same line, so ref-based bailing-out already works without any changes here. This PR does not change the observable behavior of `React.memo` at all.
How can I resolve this? If you propose a fix, please make it concise.
Comment on lines
+12
to
+14
| export function isForwardRef(type: mixed): boolean %checks { | ||
| return typeof type === 'object' && type !== null && type.$$typeof === REACT_FORWARD_REF_TYPE; | ||
| } |
There was a problem hiding this comment.
isForwardRef helper is dead code — never imported or used
The new isForwardRef export is never imported anywhere. ReactMemo.js duplicates the same check inline:
// ReactMemo.js line 28
const isForwardRefComponent = typeof type === 'object' && type !== null && type.$$typeof === REACT_FORWARD_REF_TYPE;If the intent was to share this utility, ReactMemo.js should import and use isForwardRef from this file instead of reimplementing it. As written, this export is unreachable dead code.
Prompt To Fix With AI
This is a comment left during a code review.
Path: packages/react/src/ReactForwardRef.js
Line: 12-14
Comment:
**`isForwardRef` helper is dead code — never imported or used**
The new `isForwardRef` export is never imported anywhere. `ReactMemo.js` duplicates the same check inline:
```js
// ReactMemo.js line 28
const isForwardRefComponent = typeof type === 'object' && type !== null && type.$$typeof === REACT_FORWARD_REF_TYPE;
```
If the intent was to share this utility, `ReactMemo.js` should import and use `isForwardRef` from this file instead of reimplementing it. As written, this export is unreachable dead code.
How can I resolve this? If you propose a fix, please make it concise.| export function memo<Props>( | ||
| type: React$ElementType, | ||
| compare?: (oldProps: Props, newProps: Props) => boolean, | ||
| compare?: (oldProps: Props, newProps: Props, oldRef: mixed, newRef: mixed) => boolean, |
There was a problem hiding this comment.
Misleading public API type signature change
The compare callback type has been changed to include oldRef and newRef parameters:
compare?: (oldProps: Props, newProps: Props, oldRef: mixed, newRef: mixed) => boolean,However, as described above, the reconciler never passes these arguments — they will always be undefined when compare is invoked. Any user who reads this type signature and writes a custom compare function that relies on oldRef/newRef will find those parameters are always undefined, leading to subtle, hard-to-debug bugs. The public type signature should not be changed to advertise parameters that are never populated.
Prompt To Fix With AI
This is a comment left during a code review.
Path: packages/react/src/ReactMemo.js
Line: 15
Comment:
**Misleading public API type signature change**
The `compare` callback type has been changed to include `oldRef` and `newRef` parameters:
```js
compare?: (oldProps: Props, newProps: Props, oldRef: mixed, newRef: mixed) => boolean,
```
However, as described above, the reconciler never passes these arguments — they will always be `undefined` when `compare` is invoked. Any user who reads this type signature and writes a custom `compare` function that relies on `oldRef`/`newRef` will find those parameters are always `undefined`, leading to subtle, hard-to-debug bugs. The public type signature should not be changed to advertise parameters that are never populated.
How can I resolve this? If you propose a fix, please make it concise.
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Mirror of facebook/react#36007
Original author: MorikawaSouma
Fix React.memo not working with forwardRef components
Summary
This PR fixes #17355, where
React.memodoesn't properly memoize components wrapped inReact.forwardRef. The issue occurred because the ref parameter was not being included in the shallow comparison when determining if a component should re-render.Root Cause
When a component is wrapped in
forwardRef, the ref is passed as a separate parameter to the render function. However, the existingmemoimplementation only compared props and did not consider the ref parameter, causing unnecessary re-renders even when both props and ref were unchanged.Changes Made
Added
isForwardRefhelper function (/packages/react/src/ReactForwardRef.js)$$typeofpropertyUpdated memo implementation (
/packages/react/src/ReactMemo.js)areEqualfunctions still receive all necessary parametersTest Coverage
Backward Compatibility
This change is fully backward compatible:
areEqualfunctions are still supported and receive the same parametersTest Plan
Documentation
I will follow up with a separate PR to update the
React.memodocumentation to mention this improvement and provide examples of usingmemowithforwardRefcomponents.Additional Notes
This fix addresses a long-standing issue that has been reported multiple times by the community. The implementation follows existing React patterns and maintains the same performance characteristics as the current implementation. The change is isolated to the
memoandforwardRefmodules, minimizing risk of regression.