fix: [#1581] Fixes bug where Node.getRootNode() returned null when inside a Shadow Root that was previously disconnected from the document

packages/happy-dom/src/nodes/node/Node.ts

@@ -1025,7 +1025,10 @@ export default class Node extends EventTarget {
 	 */
 	public [PropertySymbol.disconnectedFromDocument](): void {
 		this[PropertySymbol.isConnected] = false;
-		this[PropertySymbol.rootNode] = null;
+
+		if (this[PropertySymbol.nodeType] !== NodeTypeEnum.documentFragmentNode) {
+			this[PropertySymbol.rootNode] = null;
+		}
 
 		if (this[PropertySymbol.ownerDocument][PropertySymbol.activeElement] === <unknown>this) {
 			this[PropertySymbol.ownerDocument][PropertySymbol.clearCache]();

packages/happy-dom/src/nodes/shadow-root/ShadowRoot.ts

@@ -7,6 +7,7 @@ import CSSStyleSheet from '../../css/CSSStyleSheet.js';
 import HTMLElement from '../../nodes/html-element/HTMLElement.js';
 import Event from '../../event/Event.js';
 import SVGElement from '../svg-element/SVGElement.js';
+import Document from '../document/Document.js';
 
 /**
  * ShadowRoot.
@@ -165,16 +166,25 @@ export default class ShadowRoot extends DocumentFragment {
 	 * @returns Active element.
 	 */
 	public get activeElement(): HTMLElement | SVGElement | null {
-		const activeElement: HTMLElement | SVGElement =
+		let activeElement: HTMLElement | SVGElement =
 			this[PropertySymbol.ownerDocument][PropertySymbol.activeElement];
-		if (
-			activeElement &&
-			activeElement[PropertySymbol.isConnected] &&
-			activeElement.getRootNode() === this
-		) {
+
+		let rootNode: ShadowRoot | Document = <ShadowRoot | Document>activeElement?.getRootNode();
+
+		if (!rootNode || rootNode === this[PropertySymbol.ownerDocument]) {
+			return null;
+		}
+
+		if (rootNode === this) {
 			return activeElement;
 		}
-		return null;
+
+		while (rootNode && rootNode !== this) {
+			activeElement = <HTMLElement | SVGElement>(<ShadowRoot>rootNode).host;
+			rootNode = <ShadowRoot | Document>activeElement.getRootNode();
+		}
+
+		return activeElement;
 	}
 
 	/**

packages/happy-dom/test/nodes/node/Node.test.ts

@@ -366,6 +366,14 @@ describe('Node', () => {
 			const rootNode = (<ShadowRoot>customElement.shadowRoot).querySelector('span')?.getRootNode();
 
 			expect(rootNode === customElement.shadowRoot).toBe(true);
+
+			document.body.removeChild(customElement);
+
+			document.body.appendChild(customElement);
+
+			const rootNode2 = (<ShadowRoot>customElement.shadowRoot).querySelector('span')?.getRootNode();
+
+			expect(rootNode2 === customElement.shadowRoot).toBe(true);
 		});
 
 		it('Returns Document when used on a node inside a ShadowRoot and the option "composed" is set to "true".', () => {

packages/happy-dom/test/nodes/shadow-root/ShadowRoot.test.ts

@@ -218,6 +218,29 @@ describe('ShadowRoot', () => {
 
 			expect(shadowRoot.activeElement === null).toBe(true);
 		});
+
+		it('Returns the first custom element when the active element is not a child of the ShadowRoot, but is a child of a custom element within it.', () => {
+			const customElement = document.createElement('custom-element');
+			const shadowRoot = <ShadowRoot>customElement.shadowRoot;
+			const div = <HTMLElement>document.createElement('div');
+			const customElementA = document.createElement('custom-element-a');
+			const shadowRootA = <ShadowRoot>customElementA.shadowRoot;
+
+			document.body.appendChild(customElement);
+
+			shadowRoot.appendChild(customElementA);
+			shadowRootA.appendChild(div);
+
+			expect(shadowRoot.activeElement === null).toBe(true);
+
+			div.focus();
+
+			expect(shadowRoot.activeElement).toBe(customElementA);
+
+			customElementA.remove();
+
+			expect(shadowRoot.activeElement === null).toBe(true);
+		});
 	});
 
 	describe('getAnimations()', () => {