fix: [#1855] Add Symbol.iterator to CSSStyleDeclaration for iteration support

packages/happy-dom/src/css/declaration/CSSStyleDeclaration.ts

@@ -4845,6 +4845,18 @@ export default class CSSStyleDeclaration {
 		}
 	}
 
+	/**
+	 * Returns an iterator, allowing you to go through all property names contained in this object.
+	 *
+	 * @returns Iterator.
+	 */
+	public *[Symbol.iterator](): IterableIterator<string> {
+		const propertyManager = this.#getPropertyManager();
+		for (const key in propertyManager.properties) {
+			yield key;
+		}
+	}
+
 	/**
 	 * Returns item.
 	 *

packages/happy-dom/test/css/declaration/CSSStyleDeclaration.test.ts

@@ -84,6 +84,41 @@ describe('CSSStyleDeclaration', () => {
 		});
 	});
 
+	describe('[Symbol.iterator]()', () => {
+		it('Returns an iterator for property names.', () => {
+			const declaration = new CSSStyleDeclaration(PropertySymbol.illegalConstructor, window, {
+				element
+			});
+
+			element.setAttribute('style', 'color: red; font-size: 12px');
+
+			expect([...declaration]).toEqual(['color', 'font-size']);
+		});
+
+		it('Returns an empty iterator when no styles are set.', () => {
+			const declaration = new CSSStyleDeclaration(PropertySymbol.illegalConstructor, window, {
+				element
+			});
+
+			expect([...declaration]).toEqual([]);
+		});
+
+		it('Iterates expanded shorthand properties.', () => {
+			const declaration = new CSSStyleDeclaration(PropertySymbol.illegalConstructor, window, {
+				element
+			});
+
+			element.setAttribute('style', 'margin: 10px');
+
+			const keys = [...declaration];
+
+			expect(keys).toContain('margin-top');
+			expect(keys).toContain('margin-right');
+			expect(keys).toContain('margin-bottom');
+			expect(keys).toContain('margin-left');
+		});
+	});
+
 	describe('get border()', () => {
 		it('Returns style property.', () => {
 			const declaration = new CSSStyleDeclaration(PropertySymbol.illegalConstructor, window, {