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chromium/third_party/blink/web_tests/external/wpt/html/infrastructure/safe-passing-of-structured-data/shared-array-buffers/resources/iframe-messagechannel-complex.html 

<!DOCTYPE html>
<script>
  const channel = new MessageChannel();
  window.parent.postMessage({ state: "port1", data: channel.port1 }, '*', [channel.port1]);
  window.onmessage = () => window.parent.postMessage({ state: "port2", data: channel.port2 }, '*', [channel.port2]);
</script>