I actually just got my rejection from FB today. Purely JavaScript questions, no leetcode at all. If I were to rewind, I'd have focused more on purely JavaScript tricks and less on other parts of the frontend repertoire. i.e. the time I spent on CSS seems to have been a waste.
Also got rejected from AMZN back in December. Made the mistake grinding leetcode during the weeks leading up to the interview, when it turned out to be purely JS trivia.
The hardest part of interviewing as FEE seems to be the lack of sample JS interview problems available, versus say, leetcode. I feel I am pretty well versed in using JS and have pretty in-depth knowledge of the arcane workings of the language far beyond a typical developer (certainly more so than my coworkers), but just like how leetcode interviews cover cases you'll never encounter in day to day work, frontend JS interview problems seem to do the same.
That said, I don't know how much JS knowledge a typical FEE at a FAANG or similar company has. But that's one big reason I want to get into one of these companies - I'm assuming, and hoping, the level of knowledge and enthusiasm (I hate to use the word passion) is much higher at SV tech companies than outside. Most of the places I've worked (banks, finance), the JS engineers can barely explain how async stuff works in JS.