Add fragment handles to children of FragmentInstances #34935
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rickhanlonii
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Nov 3, 2025
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| function addFragmentHandleToFiber( |
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I'd gate inside these fns too
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This PR adds a `unstable_reactFragments?: Set<FragmentInstance>` property to DOM nodes that belong to a Fragment with a ref (top level host components). This allows you to access a FragmentInstance from a DOM node. This is flagged behind `enableFragmentRefsInstanceHandles`. The primary use case to unblock is reusing IntersectionObserver instances. A fairly common practice is to cache and reuse IntersectionObservers that share the same config, with a map of node->callbacks to run for each entry in the IO callback. Currently this is not possible with Fragment Ref `observeUsing` because the key in the cache would have to be the `FragmentInstance` and you can't find it without a handle from the node. This works now by accessing `entry.target.fragments`. This also opens up possibilities to use `FragmentInstance` operations in other places, such as events. We can do `event.target.unstable_reactFragments`, then access `fragmentInstance.getClientRects` for example. In a future PR, we can assign an event's `currentTarget` as the Fragment Ref for a more direct handle when the event has been dispatched by the Fragment itself. The first commit here implemented a handle only on observed elements. This is awkward because there isn't a good way to document or expose this temporary property. `element.fragments` is closer to what we would expect from a DOM API if a standard was implemented here. And by assigning it to all top-level nodes of a Fragment, it can be used beyond the cached IntersectionObserver callback. One tradeoff here is adding extra work during the creation of FragmentInstances as well as keeping track of adding/removing nodes. Previously we only track the Fiber on creation but here we add a traversal which could apply to a large set of top-level host children. The `element.unstable_reactFragments` Set can also be randomly ordered. DiffTrain build for [edd05f1](edd05f1)
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This PR adds a `unstable_reactFragments?: Set<FragmentInstance>` property to DOM nodes that belong to a Fragment with a ref (top level host components). This allows you to access a FragmentInstance from a DOM node. This is flagged behind `enableFragmentRefsInstanceHandles`. The primary use case to unblock is reusing IntersectionObserver instances. A fairly common practice is to cache and reuse IntersectionObservers that share the same config, with a map of node->callbacks to run for each entry in the IO callback. Currently this is not possible with Fragment Ref `observeUsing` because the key in the cache would have to be the `FragmentInstance` and you can't find it without a handle from the node. This works now by accessing `entry.target.fragments`. This also opens up possibilities to use `FragmentInstance` operations in other places, such as events. We can do `event.target.unstable_reactFragments`, then access `fragmentInstance.getClientRects` for example. In a future PR, we can assign an event's `currentTarget` as the Fragment Ref for a more direct handle when the event has been dispatched by the Fragment itself. The first commit here implemented a handle only on observed elements. This is awkward because there isn't a good way to document or expose this temporary property. `element.fragments` is closer to what we would expect from a DOM API if a standard was implemented here. And by assigning it to all top-level nodes of a Fragment, it can be used beyond the cached IntersectionObserver callback. One tradeoff here is adding extra work during the creation of FragmentInstances as well as keeping track of adding/removing nodes. Previously we only track the Fiber on creation but here we add a traversal which could apply to a large set of top-level host children. The `element.unstable_reactFragments` Set can also be randomly ordered. DiffTrain build for [edd05f1](edd05f1)
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This PR adds a `unstable_reactFragments?: Set<FragmentInstance>` property to DOM nodes that belong to a Fragment with a ref (top level host components). This allows you to access a FragmentInstance from a DOM node. This is flagged behind `enableFragmentRefsInstanceHandles`. The primary use case to unblock is reusing IntersectionObserver instances. A fairly common practice is to cache and reuse IntersectionObservers that share the same config, with a map of node->callbacks to run for each entry in the IO callback. Currently this is not possible with Fragment Ref `observeUsing` because the key in the cache would have to be the `FragmentInstance` and you can't find it without a handle from the node. This works now by accessing `entry.target.fragments`. This also opens up possibilities to use `FragmentInstance` operations in other places, such as events. We can do `event.target.unstable_reactFragments`, then access `fragmentInstance.getClientRects` for example. In a future PR, we can assign an event's `currentTarget` as the Fragment Ref for a more direct handle when the event has been dispatched by the Fragment itself. The first commit here implemented a handle only on observed elements. This is awkward because there isn't a good way to document or expose this temporary property. `element.fragments` is closer to what we would expect from a DOM API if a standard was implemented here. And by assigning it to all top-level nodes of a Fragment, it can be used beyond the cached IntersectionObserver callback. One tradeoff here is adding extra work during the creation of FragmentInstances as well as keeping track of adding/removing nodes. Previously we only track the Fiber on creation but here we add a traversal which could apply to a large set of top-level host children. The `element.unstable_reactFragments` Set can also be randomly ordered. DiffTrain build for [edd05f1](facebook@edd05f1)
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This PR adds a `unstable_reactFragments?: Set<FragmentInstance>` property to DOM nodes that belong to a Fragment with a ref (top level host components). This allows you to access a FragmentInstance from a DOM node. This is flagged behind `enableFragmentRefsInstanceHandles`. The primary use case to unblock is reusing IntersectionObserver instances. A fairly common practice is to cache and reuse IntersectionObservers that share the same config, with a map of node->callbacks to run for each entry in the IO callback. Currently this is not possible with Fragment Ref `observeUsing` because the key in the cache would have to be the `FragmentInstance` and you can't find it without a handle from the node. This works now by accessing `entry.target.fragments`. This also opens up possibilities to use `FragmentInstance` operations in other places, such as events. We can do `event.target.unstable_reactFragments`, then access `fragmentInstance.getClientRects` for example. In a future PR, we can assign an event's `currentTarget` as the Fragment Ref for a more direct handle when the event has been dispatched by the Fragment itself. The first commit here implemented a handle only on observed elements. This is awkward because there isn't a good way to document or expose this temporary property. `element.fragments` is closer to what we would expect from a DOM API if a standard was implemented here. And by assigning it to all top-level nodes of a Fragment, it can be used beyond the cached IntersectionObserver callback. One tradeoff here is adding extra work during the creation of FragmentInstances as well as keeping track of adding/removing nodes. Previously we only track the Fiber on creation but here we add a traversal which could apply to a large set of top-level host children. The `element.unstable_reactFragments` Set can also be randomly ordered. DiffTrain build for [edd05f1](facebook@edd05f1)
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This PR adds a
unstable_reactFragments?: Set<FragmentInstance>property to DOM nodes that belong to a Fragment with a ref (top level host components). This allows you to access a FragmentInstance from a DOM node.This is flagged behind
enableFragmentRefsInstanceHandles.The primary use case to unblock is reusing IntersectionObserver instances. A fairly common practice is to cache and reuse IntersectionObservers that share the same config, with a map of node->callbacks to run for each entry in the IO callback. Currently this is not possible with Fragment Ref
observeUsingbecause the key in the cache would have to be theFragmentInstanceand you can't find it without a handle from the node. This works now by accessingentry.target.fragments.This also opens up possibilities to use
FragmentInstanceoperations in other places, such as events. We can doevent.target.unstable_reactFragments, then accessfragmentInstance.getClientRectsfor example. In a future PR, we can assign an event'scurrentTargetas the Fragment Ref for a more direct handle when the event has been dispatched by the Fragment itself.The first commit here implemented a handle only on observed elements. This is awkward because there isn't a good way to document or expose this temporary property.
element.fragmentsis closer to what we would expect from a DOM API if a standard was implemented here. And by assigning it to all top-level nodes of a Fragment, it can be used beyond the cached IntersectionObserver callback.One tradeoff here is adding extra work during the creation of FragmentInstances as well as keeping track of adding/removing nodes. Previously we only track the Fiber on creation but here we add a traversal which could apply to a large set of top-level host children. The
element.unstable_reactFragmentsSet can also be randomly ordered.