Standard JS. It's a library maintained by one guy in Russia who went to jail for some car accident (I don't have the full context). He needed money and had trouble getting it. Then the Ukraine invasion happened and that only made it more difficult for him to get money. Also he was harassed by less technical people seeing his code on websites thinking it was malicious.
Wow I saw that my angular projects used core-js, but it seemed so massive and fundamental that I assumed it had the backing of a large company like angular itself. It's staggering to see that it was largely being held up by a single person and I hope their situation has improved since writing that blogpost. I can't even begin to imagine donating so much time and energy to a project even in spite of getting so much hate in return.