<html><head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<script>
function load() {
  function next() {
    if (count < 5)
      iframe.src = 'data:text/html;charset=utf-8,iframe ' + (++count);
  }

  var count = 0;
  var iframe = document.createElement('iframe');
  iframe.onload = function () { setTimeout(next, 0) };
  document.body.appendChild(iframe);

  setTimeout(next, 0);
}
</script>
</head>

<body onload="load()">
Testcase
</body>
</html>