Last time I stumbled on an "io game" built this way, the lack of WASM debugging tools made it very hard to hack at the game :(
Of course, people would say "what's the point" when JS is a thing and widely supported. I wonder if there'd be a) a compelling improvement in performance and b) a compelling improvement in reliability if we just wholesale replaced it based on lessons learned? I reckon even just keeping JS and eliminating implicit coercions would be a huge improvement (as well as maybe automatic semicolon insertion) and reduce the debugging times considerably.
I don't know about "less quirky", but Microsoft tried with VBScript. Google tried with Dart. Initially, Dart meant to be interpreted by the browser (not transpiled to JS). I'm sure there might have been similar, smaller projects, but Javascript-in-the-browser has momentum that's hard to beat.
I'm trying my best :D
<link rel='stylesheet' href='res/lettercrap.css' />
<link rel='stylesheet' href='res/style.css' />
;o