Fix crash when reading headlessuiFocusGuard of relatedTarget in the FocusTrap component (#2203)

* ensure `relatedTarget` is an `HTMLElement`

Or in other words, Robin trust the type system...

I was assuming that this was always an `HTMLElement` or `null` but
that's not the case. Just using `e.relatedTarget` shows that `dataset`
is not always available.

* update changelog

packages/@headlessui-react/CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix `failed to removeChild on Node` bug ([#2164](https://github.com/tailwindlabs/headlessui/pull/2164))
 - Don’t overwrite classes during SSR when rendering fragments ([#2173](https://github.com/tailwindlabs/headlessui/pull/2173))
 - Improve `Combobox` accessibility ([#2153](https://github.com/tailwindlabs/headlessui/pull/2153))
+- Fix crash when reading `headlessuiFocusGuard` of `relatedTarget` in the `FocusTrap` component ([#2203](https://github.com/tailwindlabs/headlessui/pull/2203))
 
 ## [1.7.7] - 2022-12-16
 

packages/@headlessui-react/src/components/focus-trap/focus-trap.tsx

@@ -109,8 +109,8 @@ export let FocusTrap = Object.assign(
         let allContainers = new Set(containers?.current)
         allContainers.add(container)
 
-        let relatedTarget = e.relatedTarget as HTMLElement | null
-        if (!relatedTarget) return
+        let relatedTarget = e.relatedTarget
+        if (!(relatedTarget instanceof HTMLElement)) return
 
         // Known guards, leave them alone!
         if (relatedTarget.dataset.headlessuiFocusGuard === 'true') {

packages/@headlessui-vue/CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix `Tab` key with non focusable elements in `Popover.Panel` ([#2147](https://github.com/tailwindlabs/headlessui/pull/2147))
 - Don’t overwrite classes during SSR when rendering fragments ([#2173](https://github.com/tailwindlabs/headlessui/pull/2173))
 - Improve `Combobox` accessibility ([#2153](https://github.com/tailwindlabs/headlessui/pull/2153))
+- Fix crash when reading `headlessuiFocusGuard` of `relatedTarget` in the `FocusTrap` component ([#2203](https://github.com/tailwindlabs/headlessui/pull/2203))
 
 ## [1.7.7] - 2022-12-16
 

packages/@headlessui-vue/src/components/focus-trap/focus-trap.ts

@@ -111,8 +111,8 @@ export let FocusTrap = Object.assign(
         let allContainers = new Set(props.containers?.value)
         allContainers.add(container)
 
-        let relatedTarget = e.relatedTarget as HTMLElement | null
-        if (!relatedTarget) return
+        let relatedTarget = e.relatedTarget
+        if (!(relatedTarget instanceof HTMLElement)) return
 
         // Known guards, leave them alone!
         if (relatedTarget.dataset.headlessuiFocusGuard === 'true') {