capricorn86#661@patch: Take class selector escaping into account.

packages/happy-dom/src/query-selector/SelectorItem.ts

@@ -1,11 +1,13 @@
 import DOMException from '../exception/DOMException';
 import IElement from '../nodes/element/IElement';
 import Element from '../nodes/element/Element';
+import CSSEscape from 'css.escape';
 
 const ATTRIBUTE_REGEXP =
 	/\[([a-zA-Z0-9-_]+)\]|\[([a-zA-Z0-9-_]+)([~|^$*]{0,1})[ ]*=[ ]*["']{0,1}([^"']+)["']{0,1}\]/g;
 const ATTRIBUTE_NAME_REGEXP = /[^a-zA-Z0-9-_$]/;
-const PSUEDO_REGEXP = /:([a-zA-Z-]+)\(([0-9n+-]+|odd|even)\)|:not\(([^)]+)\)|:([a-zA-Z-]+)/g;
+const PSUEDO_REGEXP =
+	/(?<!\\):([a-zA-Z-]+)\(([0-9n+-]+|odd|even)\)|(?<!\\):not\(([^)]+)\)|(?<!\\):([a-zA-Z-]+)/g;
 const CLASS_REGEXP = /\.([a-zA-Z0-9-_$]+)/g;
 const TAG_NAME_REGEXP = /^[a-zA-Z0-9-]+/;
 const ID_REGEXP = /#[A-Za-z][-A-Za-z0-9_]*/g;
@@ -294,19 +296,16 @@ export default class SelectorItem {
 		element: IElement,
 		selector: string
 	): { priorityWeight: number; matches: boolean } {
-		const regexp = new RegExp(CLASS_REGEXP, 'g');
-		const classList = element.className.split(' ');
-		const classSelector = selector.split(':')[0];
+		const classList = element.className.split(' ').map(CSSEscape);
+		const classSelector = selector.split(/(?<!\\):/g)[0];
 		let priorityWeight = 0;
-		let match: RegExpMatchArray;
-
-		while ((match = regexp.exec(classSelector))) {
+		// Still figuring the right regex for this
+		if (classSelector.startsWith('.')) {
 			priorityWeight += 10;
-			if (!classList.includes(match[1])) {
+			if (!classList.includes(classSelector.slice(1))) {
 				return { priorityWeight: 0, matches: false };
 			}
 		}
-
 		return { priorityWeight, matches: true };
 	}