Unlike plain objects, a Map accepts any key type (objects, functions, not just strings), keeps insertion order, has a real .size, and is directly iterable. Use set, get, has, delete. Reach for Map when keys aren't strings or you need frequent add/remove and size.
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<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre id="o"></pre>
<script>const m=new Map(); const key={}; m.set(key,'obj-keyed'); m.set('s',1);
document.getElementById('o').textContent='size='+m.size+' val='+m.get(key);</script></body></html>