It never occured to me to use it for indexOf, but if it works, that's nice. I usually use a bitwise OR as a faster alternative to Math.floor:
1.324324|0 // 1
Well, it's not exactly floor, as it will just cut of everything after the dot, but if you're only dealing with positive number it does the job and has the nice side effect of converting non-numbers into 0:
I just watched a trailer for the upcoming 2021 JRPG Fantasian. They demonstrated an interesting mechanic where random encounters can be sent to a stockpile instead of fighting them right away, which can be emptied in a single battle string at the player's choice of timing.