Make element returned by useOutlet have stable-ish reference

[Malien]

I was trying to accomplish an exit animation for routes rendered in <Outlet />s. I need to hold onto the previous value of outlet until it finishes its animation.

const outlet = useOutlet()
const [heldOntoNode, setHeldOntoNode] = useState(outlet)

// If outlet changes to null, don't discard `heldOntoNode`.
// Otherwise, heldOntoNode should reflect the latest value of the outlet
if (outlet && heldOntoNode !== outlet) {
  // Calling setState in render body will discard the current render
  // and schedule a new one immediately
  setHeldOntoNode(outlet)
  return null
}

if (!heldOntoNode) return null

return (
  <Modal 
    // outlet set to null means we have to hide the modal
    // aka. trigger it's exit animation.
    open={!!outlet} 
    onExitAnimationEnd={() => setHeldOntoNode(null)}
  >
    {heldOntoNode}
  </Modal>
)

Calling setState in render is THE way to capture the previous value. Reading refs in render isn't really allowed.

Since useOutlet wraps the <RenderedRoute /> in <OutletContext.Provider />, the reference to the outer <OutletContext.Provider /> is always different on every re-render. And the code above triggers an infinite render loop.

This PR just wraps the resulting element in useMemo. That's it.

The workaround for me currently involves asserting that the element is in fact the react context, and grabbing the stable children prop.

I'm not sure we can guarantee stable references from useOutlet going forward, but that would be nice.

[changeset-bot]

⚠️ No Changeset found

Latest commit: b67d239

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[remix-cla-bot]

Hi @Malien,

Welcome, and thank you for contributing to React Router!

Before we consider your pull request, we ask that you sign our Contributor License Agreement (CLA). We require this only once.

You may review the CLA and sign it by adding your name to contributors.yml.

Once the CLA is signed, the CLA Signed label will be added to the pull request.

If you have already signed the CLA and received this response in error, or if you have any questions, please contact us at [email protected].

Thanks!

- The Remix team

[remix-cla-bot]

Thank you for signing the Contributor License Agreement. Let's get this merged! 🥳