Although I personally would love to see the death of JavaScript 
, and have Julia → WebAssembly take over as the preeminent language of the web, unfortunately, no matter what much better options are available, I don’t see JS going away anytime soon - just because of the shear momentum, all the resources available (books, on-line courses, tools, coding camps, money spent to make JS run fast), and all the programmers already skilled in getting JS to do what they want, no matter whether or not they are truly happy with it.
After all (as I commented on here), COBOL and FORTRAN are still around and in heavy use 
after nearly 60 years!
I am cautiously optimistic that WA will help level the playing field, and in addition, just as LLVM has helped spark a lot of creativity in new programming languages (such as Julia itself), WA will spark just as much creativity in new languages designed for client side web programming.