Account for Shadow DOM when dealing with nested dialogs

README.md

@@ -1,6 +1,6 @@
 # [A11y Dialog](https://a11y-dialog.netlify.app)
 
-This is a lightweight (1.5Kb) yet flexible script to create accessible dialog windows.
+This is a lightweight (1.7Kb) yet flexible script to create accessible dialog windows.
 
 - [Documentation ↗](https://a11y-dialog.netlify.app)
 - [Demo on CodeSandbox ↗](https://codesandbox.io/s/a11y-dialog-v8-5gqfz8)

biome.json

@@ -10,7 +10,10 @@
     "attributePosition": "auto"
   },
   "organizeImports": { "enabled": true },
-  "linter": { "enabled": true, "rules": { "recommended": true } },
+  "linter": {
+    "enabled": true,
+    "rules": { "recommended": true, "style": { "noParameterAssign": "off" } }
+  },
   "javascript": {
     "formatter": {
       "quoteProperties": "asNeeded",

src/a11y-dialog.ts

@@ -1,4 +1,9 @@
-import { getActiveElement, moveFocusToDialog, trapTabKey } from './dom-utils'
+import {
+  closest,
+  getActiveElement,
+  moveFocusToDialog,
+  trapTabKey,
+} from './dom-utils'
 
 export type A11yDialogEvent = 'show' | 'hide' | 'destroy'
 export type A11yDialogInstance = InstanceType<typeof A11yDialog>
@@ -192,8 +197,9 @@ export default class A11yDialog {
    */
   private bindKeypress(event: KeyboardEvent) {
     // This is an escape hatch in case there are nested open dialogs, so that
-    // only the top most dialog gets interacted with
-    if (document.activeElement?.closest('[aria-modal="true"]') !== this.$el) {
+    // only the top most dialog gets interacted with (`closest` is basically
+    // `Element.prototype.closest()` accounting for Shadow DOM subtrees)
+    if (closest('[aria-modal="true"]', getActiveElement()) !== this.$el) {
       return
     }
 

src/dom-utils.ts

@@ -213,3 +213,22 @@ export function trapTabKey(el: HTMLElement, event: KeyboardEvent) {
     event.preventDefault()
   }
 }
+
+/**
+ * Find the closest element to the given element matching the given selector,
+ * accounting for Shadow DOM subtrees.
+ * @author Louis St-Amour
+ * @see: https://stackoverflow.com/a/56105394
+ */
+export function closest(selector: string, base: Element | null) {
+  function from(el: Element | Window | Document | null): Element | null {
+    if (!el || el === document || el === window) return null
+    if ((el as Slottable).assignedSlot) el = (el as Slottable).assignedSlot
+    return (
+      (el as Element).closest(selector) ||
+      from(((el as Element).getRootNode() as ShadowRoot).host)
+    )
+  }
+
+  return from(base)
+}