index.html

<script>

  // Run before loading iframe-resizer
(function detectProtoPollution() {
  const safe = {};
  const marker = "PROTO_POLLUTION_TEST_" + Math.random();

  // Try to pollute
  JSON.parse(`{"__proto__": {"${marker}": true}}`);

  const polluted = ({}).hasOwnProperty(marker) || safe[marker] === true;

  if (polluted) {
    console.error("[!] PROTOTYPE POLLUTION DETECTED! Environment is vulnerable.");
  } else {
    console.log("[+] Safe from __proto__ pollution via JSON.parse");
  }
})();
</script>