postMessage_override_helper.html

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<!DOCTYPE html>

<html>

<head>

  <title>Overriding postMessage and dispatchEvent bindings</title>

  <script type="application/javascript">

    window.postMessage = function (evt) {

      window.parent.postMessage("FAIL overridden postMessage called", "*");

};

    var count = 0;

    function receiveMessage(evt) {

      count++;

      if (count == 2) {

        window.dispatchEvent = function(evt) {

          window.parent.postMessage("FAIL", "*");

          throw "dispatchEvent threw";

};

      window.parent.postMessage(evt.data, "http://mochi.test:8888");

    function setup() {

      var target = document.getElementById("location");

      target.textContent = location.hostname + ":" + (location.port || 80);

    window.addEventListener("message", receiveMessage);

    window.addEventListener("load", setup);

  </script>

</head>

<body>

<h1 id="location">No location!</h1>

</body>

</html>