[DOM] Handle blur on Fragments below Document - #37062
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The PR fixes handling blur events on Fragments below the Document by properly accounting for the document context via getOwnerDocumentFromRootContainer. The changes are minimal, coherent, and backed by a new test case to ensure the behavior is correct. Everything aligns with the contribution guidelines and seems ready to merge.
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… a Document When a FragmentInstance's nearest host parent fiber is the HostRoot, `getInstanceFromHostFiber` returns the root's `Container`. `blur()` reads `parentHostInstance.ownerDocument.activeElement` from it, but a `Document` container's `ownerDocument` is null, so the read throws. The test mounts the fragment above the `<html>` element of a root created on the document, where the nearest host parent is always the HostRoot. This keeps the coverage intact even once HostSingleton fibers are treated as host parents, which will stop fragments mounted under `<body>` from falling back to the root. The test pins down the current throwing behavior. The fix in the next commit flips it to asserting that the focused child inside the fragment actually loses focus. Co-Authored-By: Claude Fable 5 <[email protected]>
When a FragmentInstance's nearest host parent fiber is the HostRoot, `blur()` read `parentInstanceOrContainer.ownerDocument.activeElement` from the root's `Container`. A `Document` container's `ownerDocument` is null, so the read threw for fragments whose nearest host parent resolves to a root mounted on the document. The owner document is now resolved with the existing `getOwnerDocumentFromRootContainer` helper, which returns the container itself when it is a `Document`. The `contains(activeElement)` check and the rest of the flow already work on a `Document`. The test from the previous commit flips from asserting the throw to asserting that the focused child inside the fragment loses focus. Co-Authored-By: Claude Fable 5 <[email protected]>
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When we
blur, we check first if the active element is even within the Fragment to avoid having to traverse the whole subtree.However, assuming
ownerDocumentreturns aDocumentis incorrect for the cases where theNodeis aDocument. Then theownerDocumentisnull. We need to handle that case to avoidCannot read properties of null (reading 'activeElement').