The following code throws "Uncaught TypeError: Cannot read properties of undefined (reading 'undefined')" when it should show 123. What am I doing wrong? I asked a similar question here Symbols and cross realms but nobody answered my specific question about cross realms
<body>
<iframe srcdoc="<script>var sym = Symbol(); var obj = {}; obj[sym] = 123;</script>">
</iframe>
<script>
const iframe = document.querySelector('iframe');
const content = iframe.contentWindow;
const value = content.obj[content.sym]; // undefined
</script>
</body>