JS as target will always be slower and bigger(as payload) than WASM as target so my point is that JS as compilation target is no longer relevant once WASM is supported(i.e. most likely by the end of the year). It makes little sense to start a javascript backend now unless you are looking for very short term benefits.
It's JavaScript that's a much smaller and faster payload if you need garbage collection. There's talk of putting a generic garbage collector into WASM but that's still well into the future. WASM also doesn't have direct access to the DOM - right now it's more like Flash or Java applets than it is JavaScript.
Edit: It's on the roadmap just after MVP so I wouldn't say it's that far. Also based on the latest talks from Luke at City Hall(I can't find the link) the access to DOM could arrive even sooner than the GC. My point is that wasm is worth investing it because it's the future. Once language X compiles to wasm and perl compiles to JS you can see a double digits performance difference. I don't need to tell you which language looks more appealing. WASM has nothing to do with applets/flash etc. It was already clarified in various posts.
The github repo for rakudo-js dates to September 2012. You're correct, but it looks like this effort has been in development for longer than WASM has been around.
> Perl 6 -> wasm won't be happening any time soon
> for now wasm is just bytecode asm.js
> if we really wanted to compile to it we would have to use enscripten and run MoarVM on top of wasm
[1] https://irclog.perlgeek.de/perl6/2016-04-15/text
[2] https://github.com/pmurias/rakudo-js