It's an IR that currently is compatible with JS, but that's not necessarily the case longterm. And I personally don't see how it can retain that property while adding some of the things the platform needs (e.g. thread support that works for existing codebases). I asked dherman this elsewhere in the thread, and it seems like diverging from JS hasn't been ruled out. https://news.ycombinator.com/item?id=6023902
So, my concern here is that asm.js will either be forced to diverge from JS to make it generally useful, or it will need to add APIs to JS that are not appropriate outside of asm.js. If it gets to that place, then I feel that the compromises necessary for asm.js were a waste, and it would have clearly been better to just introduce a new IR that wasn't bound by the constraints of asm.js.
The fact is that asm.js runs and as of recently, does so performantly in Chrome which does even implement the aot optimisations in odinmonkey.
To my mind given the above fact it seems perfectly reasonable to make the assertion that asm.js is just javascript.