fix: prevent invalid child combinators in shadow DOM

refs #1100

Author: fczbkk

src/selector-nth-child.ts

@@ -7,7 +7,8 @@ import { getIntersection } from "./utilities-data.js";
 export function getElementNthChildSelector(
   element: Element,
 ): CssSelectorGenerated[] {
-  const siblings = element.parentElement?.children;
+  const parent = element.parentNode;
+  const siblings = parent && "children" in parent ? parent.children : null;
   if (siblings) {
     for (let i = 0; i < siblings.length; i++) {
       if (siblings[i] === element) {

src/selector-nth-of-type.ts

@@ -9,7 +9,8 @@ export function getElementNthOfTypeSelector(
   element: Element,
 ): CssSelectorGenerated[] {
   const tag = getTagSelector([element])[0];
-  const parentElement = element.parentElement;
+  const parent = element.parentNode;
+  const parentElement = parent && "children" in parent ? parent : null;
 
   if (parentElement) {
     const siblings = Array.from(parentElement.children).filter(

test/shadow-dom.spec.ts

@@ -1,6 +1,7 @@
 import { assert } from "chai";
 import { getCssSelector } from "../src";
 import { getIdSelector } from "../src/selector-id.js";
+import { testSelector } from "../src/utilities-dom";
 
 describe("Shadow DOM", () => {
   let root: Element;
@@ -33,4 +34,17 @@ describe("Shadow DOM", () => {
     const result = getIdSelector([shadowElement])[0];
     assert.equal(result, "#shadowElement");
   });
+
+  it("should not generate invalid selectors for shadow root children without identifiers", () => {
+    // force creation of a fallback selector
+    shadowRoot.replaceChildren();
+    const testElement = shadowRoot.appendChild(document.createElement("div"));
+    shadowRoot.appendChild(document.createElement("div"));
+
+    const result = getCssSelector(testElement, { root: shadowRoot });
+
+    assert.notMatch(result, />\s*>/); // consecutive child combinators
+    assert.notMatch(result, />\s*$/); // trailing child combinator
+    assert.ok(testSelector([testElement], result, shadowRoot));
+  });
 });