I understand that. Take a read of this:
http://mrale.ph/blog/2013/03/28/why-asmjs-bothers-me.html.
I have a lot of respect for Egorov, and I agree with his views on this matter quite entirely.
The sole benefit of embedding a bytecode in a language is that you get the side effect that it can run anywhere that language runs. But in general, this implies performance penalties, especially when the language is relatively slow to begin with.
But in this case, this demo is made usable (ie: the impressive part) by writing a compiler specifically for the bytecode itself. So it works well in spite of the fact that it's a bytecode embedded in JS, not because of it. The really cool things about this demo are precisely 2 things:
1. asm.js makes running C++ code that would render to OpenGL in the browser a possibility, and with relatively good performance. Kudos to Mozilla.
2. It runs on browsers that don't know about asm.js, but it's effectively an emulated machine, and it's slow.
I just take issue with calling this an example of what JavaScript/HTML5 can do. I think seeing an application written in JS using WebGL or Canvas as something much more impressive, and there are Q3 renderers that are natively JS that run with amazing performance in the browser. This is just dressing up the fact that turing completeness is a thing and calling attention to it. The real thing to get from this demo is that there are enormous benefits to having a bytecode for the web over trying to optimize a fully dynamic language like JS. I feel like that is relatively lost by the title.