Codebase Browser
chromium
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chromium/chrome/test/data/devtools/oopif.html 

<body>
  <iframe width=300px height=300px></iframe>
  <script>
    var url = window.location.href;
    url = url.replace(/a\.com/, "b.com");
    url = url.replace(/oopif\.html/, "oopif_frame.html");
    document.querySelector('iframe').setAttribute('src', url);
  </script>
</body>