Fix potential dangerous access of ref value in useEffect cleanup #7404
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Directly accessing the value of a ref in a `useEffect` cleanup function can lead to problems, as refs "live" outside of React's rendering cycle and it can therefore happen that the value of the ref changes between the first execution and the cleanup.
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Follow up: #7406 tl;dr: Refs should probably not be used at all in this case. I would still appreciate it if this PR could be merged as it fixes an immediate bug I have in my code. |
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Thanks! |
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Directly accessing the value of a ref in a
useEffectcleanup function can lead to problems, as refs “live” outside of React's rendering cycle and it can therefore happen that the value of the ref changes between the first execution and the cleanup.See ESLint warning:
This is not just a theoretical problem. I encountered a bug after upgrading to React 19 while running in dev mode. My callback passed to the
onChangeprop of aSlidercomponent (which usesuseMoveinternally) was not updated and therefore used a stale variable that was captured by the closure. I believe this is related to React calling the useEffect hooks twice in development mode, although I'm not sure why this only happens with React 19 and not React 18, which introduced this behavior.