1 files changed, 24 insertions, 0 deletions
diff --git a/testing/web-platform/tests/html/webappapis/dynamic-markup-insertion/document-write/during-readystatechange.window.js b/testing/web-platform/tests/html/webappapis/dynamic-markup-insertion/document-write/during-readystatechange.window.js
new file mode 100644
index 0000000000..49d5051c25
--- /dev/null
+++ b/testing/web-platform/tests/html/webappapis/dynamic-markup-insertion/document-write/during-readystatechange.window.js
@@ -0,0 +1,24 @@
+// This tests whether the insertion point gets reset before or after the readystatechange event.
+// See https://github.com/whatwg/html/pull/6613#discussion_r620171070.
+// Recall that resetting the insertion point means that document.write() performs the document open
+// steps and blows away previous content in the document.
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => { frame.remove(); });
+  frame.src = "../opening-the-input-stream/resources/dummy.html";
+  frame.onload = t.step_func_done(() => {
+    const states = [];
+    frame.contentDocument.onreadystatechange = t.step_func(() => {
+      if (frame.contentDocument.readyState === "interactive") {
+        assert_not_equals(frame.contentDocument.textContent, "", "Precondition check: dummy document is not empty");
+
+        frame.contentDocument.write("Some text");
+
+        // If the insertion point is reset before the readystatechange handler, then the
+        // document.write() call above will blow away the text originally in dummy.html, leaving only what we wrote.
+        assert_equals(frame.contentDocument.textContent, "Some text");
+      }
+    });
+  });
+}, "document.write() during readystatechange to interactive");