1 files changed, 16 insertions, 0 deletions
diff --git a/testing/web-platform/tests/resources/declarative-shadow-dom-polyfill.js b/testing/web-platform/tests/resources/declarative-shadow-dom-polyfill.js
new file mode 100644
index 0000000000..dfb0a1e053
--- /dev/null
+++ b/testing/web-platform/tests/resources/declarative-shadow-dom-polyfill.js
@@ -0,0 +1,16 @@
+/*
+ * Polyfill for attaching shadow trees for declarative Shadow DOM for implementations that do not support
+ * declarative Shadow DOM.
+ *
+ * root: The root of the subtree to perform the attachments in
+ */
+
+function polyfill_declarative_shadow_dom(root) {
+  root.querySelectorAll("template[shadowroot]").forEach(template => {
+    const mode = template.getAttribute("shadowroot");
+    const shadowRoot = template.parentNode.attachShadow({ mode });
+    shadowRoot.appendChild(template.content);
+    template.remove();
+    polyfill_declarative_shadow_dom(shadowRoot);
+  });
+}