[klibertp]

> Why would normal JS developers be writing in asm.js? Do you even understand why asm.js exists?

asm.js is a compiler target, true. Is it really that much C specific? Isn't it possible to compile parts of JavaScript to asm.js? For example the parts which deal with drawing - computing points of - complex things on a canvas? That would be a good reason for JS devs to use asm.js - of course via a compiler, but if that's not available, I can imagine some people doing this by hand. Remember that people used to code in real asm all the time a few centuries ago.

[TazeTSchnitzel]

> asm.js is a compiler target, true. Is it really that much C specific?

No, but I'd say it's low-level language specific. C, C++, Pascal, Swift, Go, D and the like. Not C# or Java.

> Isn't it possible to compile parts of JavaScript to asm.js?

Yes... asm.js, which is a subset of JS, can be compiled to asm.js. You can compile any language to itself. There's no real point in doing so, however.

More seriously, no, not really. JS is a dynamic language. It can't be compiled ahead-of-time.

> For example the parts which deal with drawing - computing points of - complex things on a canvas?

No, you couldn't compile that to native code. If you tried, I doubt it'd be faster than your browser's existing JIT.

> That would be a good reason for JS devs to use asm.js - of course via a compiler, but if that's not available, I can imagine some people doing this by hand. Remember that people used to code in real asm all the time a few centuries ago.

You could hand-write asm.js, but it'd be difficult. Manually manipulating the heap and stack isn't fun. There's no memory allocator included. It would make far more sense to just write in C, compile it, and write glue code, or just to write easily JIT-ed JS in the first place.

[klibertp]

> Yes... asm.js, which is a subset of JS, can be compiled to asm.js. You can compile any language to itself. There's no real point in doing so, however.

Tell this to Google Closure Compiler folks :)

> More seriously, no, not really. JS is a dynamic language. It can't be compiled ahead-of-time.

I don't think that's true. For a counter-example consider Dylan: it's AOT compiled to binary, yet it's rather dynamic. There are many AOT compiled Scheme implementations, and Scheme is rather dynamic, too. I think you can AOT compile everything, it's just a matter of how huge a runtime you'll need to provide. There's probably a point where it's more trouble than it's worth, but in principle you should be able to compile anything. Asm itself is very dynamic language, with dynamic code generation, code rewriting or dynamic evaluation all over the place, so I really don't think there's anything preventing you from doing so. Besides how impractical that would be, of course :)

But I wasn't actually thinking of JS as a whole, but of some specific, computation-related subset of it.

For example, let's assume that I'm writing a function and I promise to only use integers in certain range and arrays with elements of same type and with fixed, immutable length. I promise never to divide by 0, and never trigger overflow, and never access an array out of bonds. It seems very restricted, but actually that's rather common in some domains. Knowing these restrictions I'd probably be able to compile my function to asm.js and have it AOT compiled, bypassing JIT, avoiding some overhead and - most importantly - knowing exactly what optimizations were used (because it was optimized by my "crippled.js" -> "asm.js" compiler).

I think I saw this idea being implemented in a couple of languages, but I don't remember exactly when it was.

Oh, and I have nothing against manual memory manipulation. I rather enjoyed working with asm on some platforms and I'm very fond of Forth. But that's me, I don't expect others to like it too.

[azakai]

> No, but I'd say it's low-level language specific. C, C++, Pascal, Swift, Go, D and the like. Not C# or Java.

asm.js is directly relatable to something like C, yes. But languages like C# are possible as well, if you add another step. For example, Unity compile C# into C++, then C++ into asm.js.

This would be even harder for arbitrary JS, of course, as it's much more dynamic than C#. Still, it would be an interesting experiment.

[TazeTSchnitzel]

I'm not sure you really can compile C# directly to native code. A subset, maybe, but not C# proper.

[azakai]

Yes, I think it's a subset, some of the more dynamic things are probably not supported.