아이프레임 자동높이 재질문

<iframe src="01.html" id="myiframe" scrolling="no" width="300"></iframe>
<script type="text/javascript">
  let iframe = document.getElementById('myiframe');
  
  window.addEventListener('message', function(e) {
    let message = e.data;
    iframe.style.height = message.height + "px";
  } , false);
</script>

<script type="text/javascript">
window.addEventListener('load', function() {
  let message = {height: document.body.scrollHeight};    
  window.top.postMessage(message, "*");
});
</script>
 
<div style="height:500px; background:#ccc;">
<a href="02.html">이동</a>
</div>

<script type="text/javascript">
window.addEventListener('load', function() {
  let message = {height: document.body.scrollHeight};    
  window.top.postMessage(message, "*");
});
</script>
 
<div style="height:300px; background:#555;">
<a href="01.html">이동</a>
</div>