Very interesting about WeakMap and WeakSet. Never knew such data structures existed. So its the best place to dump stuff that you might need later but just too much maintainence to handle. Its like a having a room left untidy by your clothes,bedsheets and stuff which is cleaned regulalry by the hotel service instead of you.

Similarly, you should not keep any valuables in the hotel suite incase they are not found anymore. Same goes for the data that is critical and you deal with care.

I feel you could explain the relevance of the Symbol class with a few more interesting applications. My recall on that topic hasn't been much after reading this. But great job after all! The rest of the article was impressive.