fix: [#1647] Fixes problem with children of created documents not being considered as connected to the DOM that was introduced in v16

packages/happy-dom/src/css/rules/CSSStyleRule.ts

@@ -7,8 +7,8 @@ import CSSStyleDeclaration from '../declaration/CSSStyleDeclaration.js';
  */
 export default class CSSStyleRule extends CSSRule {
 	public readonly type = CSSRule.STYLE_RULE;
-	public readonly selectorText = '';
 	public readonly styleMap = new Map();
+	public selectorText = '';
 	public [PropertySymbol.cssText] = '';
 	#style: CSSStyleDeclaration | null = null;
 

packages/happy-dom/src/nodes/document/Document.ts

@@ -65,7 +65,7 @@ export default class Document extends Node {
 	public [PropertySymbol.isFirstWrite] = true;
 	public [PropertySymbol.isFirstWriteAfterOpen] = false;
 	public [PropertySymbol.nodeType] = NodeTypeEnum.documentNode;
-	public [PropertySymbol.isConnected] = false;
+	public [PropertySymbol.isConnected] = true;
 	public [PropertySymbol.adoptedStyleSheets]: CSSStyleSheet[] = [];
 	public [PropertySymbol.implementation] = new DOMImplementation(this);
 	public [PropertySymbol.readyState] = DocumentReadyStateEnum.interactive;

packages/happy-dom/src/nodes/html-element/HTMLElement.ts

@@ -613,10 +613,15 @@ export default class HTMLElement extends Element {
 	public override [PropertySymbol.connectedToDocument](): void {
 		super[PropertySymbol.connectedToDocument]();
 
-		this[PropertySymbol.window][PropertySymbol.customElementReactionStack].enqueueReaction(
-			this,
-			'connectedCallback'
-		);
+		if (
+			this[PropertySymbol.ownerDocument][PropertySymbol.window].document ===
+			this[PropertySymbol.ownerDocument]
+		) {
+			this[PropertySymbol.window][PropertySymbol.customElementReactionStack].enqueueReaction(
+				this,
+				'connectedCallback'
+			);
+		}
 	}
 
 	/**
@@ -625,10 +630,15 @@ export default class HTMLElement extends Element {
 	public override [PropertySymbol.disconnectedFromDocument](): void {
 		super[PropertySymbol.disconnectedFromDocument]();
 
-		this[PropertySymbol.window][PropertySymbol.customElementReactionStack].enqueueReaction(
-			this,
-			'disconnectedCallback'
-		);
+		if (
+			this[PropertySymbol.ownerDocument][PropertySymbol.window].document ===
+			this[PropertySymbol.ownerDocument]
+		) {
+			this[PropertySymbol.window][PropertySymbol.customElementReactionStack].enqueueReaction(
+				this,
+				'disconnectedCallback'
+			);
+		}
 	}
 
 	/**

packages/happy-dom/src/window/BrowserWindow.ts

@@ -835,17 +835,6 @@ export default class BrowserWindow extends EventTarget implements INodeJSGlobal
 		// Document
 		this.document = new this.HTMLDocument();
 		this.document[PropertySymbol.defaultView] = this;
-		this.document[PropertySymbol.isConnected] = true;
-
-		this.document[PropertySymbol.nodeArray][0][PropertySymbol.isConnected] = true;
-
-		this.document[PropertySymbol.nodeArray][0][PropertySymbol.nodeArray][0][
-			PropertySymbol.isConnected
-		] = true;
-
-		this.document[PropertySymbol.nodeArray][0][PropertySymbol.nodeArray][1][
-			PropertySymbol.isConnected
-		] = true;
 
 		// Ready state manager
 		this[PropertySymbol.readyStateManager].waitUntilComplete().then(() => {

packages/happy-dom/test/dom-parser/DOMParser.test.ts

@@ -259,7 +259,7 @@ describe('DOMParser', () => {
 				'text/html'
 			);
 
-			expect(newDocument.isConnected).toBe(false);
+			expect(newDocument.isConnected).toBe(true);
 			expect(newDocument.defaultView).toBe(window);
 
 			const customElement = <CustomElement>newDocument.querySelector('custom-element');

packages/happy-dom/test/nodes/html-style-element/HTMLStyleElement.test.ts

@@ -3,6 +3,8 @@
 import HTMLStyleElement from '../../../src/nodes/html-style-element/HTMLStyleElement.js';
 import { beforeEach, describe, it, expect } from 'vitest';
 import HTMLElement from '../../../src/nodes/html-element/HTMLElement.js';
+import DOMImplementation from '../../../src/dom-implementation/DOMImplementation.js';
+import CSSStyleRule from '../../../src/css/rules/CSSStyleRule.js';
 
 describe('HTMLStyleElement', () => {
 	let window: Window;
@@ -185,5 +187,73 @@
 
 			expect(documentElementComputedStyle.backgroundColor).toBe('blue');
 		});
+
+		it('Returns an CSSStyleSheet instance with its text content as style rules for #1647.', () => {
+			const StyleTagRegexp = /<style[^>]*>(?<content>.*?)<\/style>/gis;
+
+			function getScopedCssRules(html: string, scope: string, dom?: DOMImplementation): string {
+				const css = Array.from(html.matchAll(StyleTagRegexp))
+					.map(({ groups }) => groups?.content ?? '')
+					.join('\n');
+
+				if (!css) {
+					return '';
+				}
+
+				// Use the browser's CSSOM to parse CSS
+				const doc = (dom ?? document.implementation).createHTMLDocument();
+				const styleElement = doc.createElement('style');
+				styleElement.textContent = css;
+				doc.body.appendChild(styleElement);
+
+				return Array.from(styleElement.sheet?.cssRules ?? [])
+					.map((rule) => {
+						if (rule instanceof CSSStyleRule) {
+							rule.selectorText = rule.selectorText
+								.split(',')
+								.map((selector) => `${scope} ${selector}`)
+								.join(',');
+						}
+
+						return rule.cssText;
+					})
+					.join('\n');
+			}
+
+			function scopeCssSelectors(html: string, scope: string, dom?: DOMImplementation): string {
+				const scopedCss = getScopedCssRules(html, scope, dom);
+
+				return `${scopedCss ? `<style>${scopedCss}</style>` : ''}${html.replace(
+					StyleTagRegexp,
+					''
+				)}`;
+			}
+
+			const html = `
+                <style>
+                #document h1, #document h2 {
+                    background: red;
+                }
+                </style>
+
+                <h1>I love this</h1>
+
+                <STYLE type="text/css">
+                h3 {
+                    color: white;
+                }
+                </STYLE>
+            `;
+
+			expect(scopeCssSelectors(html, '.scope'))
+				.toEqual(`<style>.scope #document h1,.scope  #document h2 { background: red; }
+.scope h3 { color: white; }</style>
+
+
+                <h1>I love this</h1>
+
+
+            `);
+		});
 	});
 });