[Refefer]

Most of the negatives are heavily focused on implementation rather than design, which I don't disagree with. However, the positives of targeting any language at a stable byte code is incredibly valuable... such as an implementation of javascript itself. A bytecode approach provides a superset to our current status quo.

That said, as browsers act more like operating systems, it makes me wonder if we've somewhat missed the point.

I agree with you about starting from scratch. I think if history is any indication, ultimately we'll end up having to write a new 'web' with very different semantics and design philosophies; goodness knows the old metaphor is starting to creak in a number of problematic ways.

[azakai]

> However, the positives of targeting any language at a stable byte code is incredibly valuable... such as an implementation of javascript itself. A bytecode approach provides a superset to our current status quo.

Not necessarily, it depends which bytecode. For example the bytecode in PNaCl, which is based on LLVM IR, is excellent for C and related languages, but not for many other important languages.

Worth reading this about the limitations of LLVM IR as a bytecode: http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-October/0437...

I've also written a post about the limitations of any single bytecode to achieve all the goals the web needs: http://mozakai.blogspot.com/2013/05/the-elusive-universal-we...

[BrendanEich]

Java has a bytecode for its client embedding; so does Flash ActionScript. This led to trouble. From http://brendaneich.github.io/Strange-Loop-2012/#/27, some pros for JS and cons for bytecode:

* Dynamic typing ⇒ no verification

* Type inference ⇒ delayed optimization

* Would bytecode compress as well?

* Bytecode standardization would suck

* Bytecode versioning would suck more

* Low-level bytecode is future-hostile

Remember Java bytecode backward compatibility hampering language evolution, in the generics (erasure) debate and result. Then they broke bytecode compat anyway.

Flash has two language implementations in it, one for AS2 and the other (Tamarin) for AS3. Only way to be sure about AS2 compat!

In many ways, with JS you have one problem; add bytecode and now you have two.

[drdaeman]

But asm.js is a bytecode, isn't it? Just with a clever-but-weird encoding that allows a backward compatibility.

In a same manner, one can deliver, for example, an x86 bytecode in JS-encoded form. Just encode opcodes as, say, "eax = 1" instead of "\xB8\x01\0\0\0".

[BrendanEich]

No, asm.js is a JS subset. "bytecode" as boosted here would be a non-subset, like JVML to Java source.

Sure, bits is bits. Doesn't matter if you're after gzipped good results. But bytecode hopes spring eternal and the hopers do not want gzipped, minified, Emscripten-produced asm.js. They want a different syntax.

[lucian1900]

In all the ways that matter, asm.js is a bytecode with a funny encoding and peculiar semantics related to that. Denying it doesn't really help.

We're all wishing for a sane bytecode for a change. It's not just syntax.

[BrendanEich]

You didn't respond to the "now you have two problems" point.

Keeping asm.js a subset of JS avoids all the back-compat-locking/future-hostile-lowering problems. And engines have only one parser to make super-fast. (Already there.)

This is a significant win. What your "sane" means is mostly aesthetics. asm.js already has int32 and uint32 conversions and casts. There is no big semantic gap for vanilla C/C++ source to JS. Typed array views help a lot here; JS's built-in operators and a few helpers in ES6 (Math.imul, polyfillable) do the rest.

The non-vanilla gaps of note are mostly gaps in JS (e.g., int64, uint64, SIMD), which we're filling in ES7 for many reasons.

Shared memory threads are indeed a gap to confine to a checked subset, not push into JS along with data races (VM-level and usercode-level -- this is fatal). We're working on that too, but it's not a "bytecode" issue _per se_.

If you continue to believe that "it's not just syntax", and you have something in the way of semantics other than the above in mind, please state it explicitly.

[lucian1900]

I was thinking of int types, SIMD, shared memory with an explicit model, and arbitrary jumps. It's nice that some of those are getting fixed.

I would also like to see a bytecode with structures (and alignment control), nice code generation and execution and some form of virtual memory for resources.

What I don't understand is why Mozilla didn't define a bytecode and a to-JS compiler for it. Browsers without support would have been just as slow, but there would have been much more room for evolution.

I'm almost expecting Mozilla to pull a Trojan any day now: define a bytecode that compiles to asm.js and declare asm.js deprecated.

[pacala]

JVML is not a bytecode. The bytecode syntax is just a disguise . JVML is a high level language that prescribes a certain object / method / inheritance model. Methods are associated with objects according to specific vtable / vinterface rules.

OTOH, asm.js is defined in terms of value types + function pointers. Just call the function pointer with the right arguments. Bring whichever objects / closures you like.

PS. Gripe of the day: 64bit computing is here (even ARM supports it) and asm.js doesn't seem to be prepared.

[BrendanEich]

Lack of 64-bit ints is a JS problem, asm.js gets them via ES7. See

https://bugzilla.mozilla.org/show_bug.cgi?id=749786

and the value objects strawman under construction for ES7.

[drdaeman]

> No, asm.js is a JS subset. "bytecode" as boosted here would be a non-subset, like JVML to Java source.

Sorry for quoting Wikipedia, but bytecode is just a form of instruction set designed for efficient execution by a software interpreter.

Maybe I'm mistaken on this, but from reading about asm.js I got an impression that asm.js-aware browsers use different approach to asm.js code and treat it more like a weirdly-encoded bytecode, not as an ordirary JS source. Or I'm misunderstanding things?

If so, asm.js is a bytecode. Whenever there's a correspondence between it and other languages doesn't matter for determining if it's bytecode or not, it's another (useful, but not related to being bytecode) property.

> They want a different syntax.

I don't think syntax matters that much, it's mostly semantics. Probably.

[Skinney]

actually, asm.js is just javascript. Basically, Mozilla looked at what sort of javascript code that the different JIT's allready handle really well, and made a specification out of it. So even in Chrome, asm.js will run very efficiently. Mozilla figuered out a way to write javascript code that made type-information easy to extract, which again makes it easy to AOT-compile. For instance, the following code:

    function asmjs(i) {
        i = i|0;
        return (i + 1)|0;
    }

is valid javascript, and you can easily write this in your own programs. The "|0" means that the variable will be converted to a integer, because it is specified in the javascript standard. As an optimization, you can use this as a type annotation, kind of like writing "int i = 0;" This is what asm.js is in a nutshell, and why it's so easy to implement a special compiler for it.

[BrendanEich]

You are replacing the "bytecode" objection, which is about syntax, with your own non-objection equating asm.js with a bytecode like JVML. I'm happy you're ok with asm.js, but those who are not, and who demand "bytecode", do care about syntax first.