One thing that I like about Lua over Javascript is how self-documenting, fun to write, and easy to read it is. It has a very simple syntax, but the extensibility of its core structures (like tables) let you accomplish a lot with that simplicity.
Its 3rd-party libraries also tend to be closer to C/C++'s "drop-in" solutions like STB[1] than the enormous JS ecosystem which often requires extra tools like Node and/or extra packages like JQuery.
Admittedly, Lua's ecosystem is much smaller than Javascript's, but in my experience Lua is vastly easier to maintain. You can certainly write bad Lua, but it's one of the only languages where I don't implicitly dread reading other people's code.
It is sort of annoying that tables which are treated like arrays are 1-indexed by convention, though.