Codebase Browser
chromium
Go to App

chromium/third_party/blink/web_tests/external/wpt/html/browsers/windows/nested-browsing-contexts/resources/frameElement-sibling-accessor.html 

<!DOCTYPE html>
<meta charset="utf-8">
<title>This page will attempt to access the frameElement of its sibling and report the results on request</title>

<h1>I did get loaded</h1>

<script>
"use strict";

window.onmessage = e => {
  const { newDocumentDomain } = e.data;
  if (newDocumentDomain) {
    document.domain = newDocumentDomain;
  }

  const siblingWindow = parent.frames[0];

  try {
    const { frameElement } = siblingWindow;

    let result = "something wierd happened";
    if (frameElement === null) {
      result = "null";
    } else if (frameElement.constructor) {
      result = frameElement.constructor.name;
    }

    parent.postMessage(result, "*");
  } catch (e) {
    parent.postMessage(e.name, "*");
  }
};
</script>