Layers of Confusion
I missed a Plus post by Ian Hickson back from August but I saw it today through the magic of the twitters. It contains quite a lot to quibble about, but I want to home in on something he wrote in the comments in response to Will Sargent, RE: one of my posts on layering in the platform:
...I don't really share his vision. I think JS is an important part of the Web, but I don't see it as any more core to the Web than CSS, HTML, the DOM APIs, HTTP, etc. Most of the proposals I've seen to take JS and build a platform on it tend to fall down on #3, #4, and #5. In particular, I think fundamentally #3 and #4 basically force the platform to have a declarative part (the declarative XAML part of .NET is how it managed to address #4, for instance, and the declarative design of XHTML2 and RDF are how they manage to address #3). That doesn't have to mean that the code part is a secondary part, though. I think the Web has reached a point where you can think of the DOM as the core, with JS and the HTML syntax layered atop that (much like how in .NET there's objects that can be represented in XAML or generated from C#), which puts the JS part on par with the HTML part in terms of importance to the platform.
This is either me not articulating my "vision" clearly, Hixie mis-understanding my point(s), or some combination thereof. So I'll try again in 4 paragraphs:
I make no claims about the relative importance of HTML, CSS, JS, DOM or any of the rest. It honestly feels silly to talk about the platform that way. I argue something very, very different: HTML, DOM, and (to a lesser extent) CSS should all conceptually bottom out at JS. I'm not saying "go write a browser in JS"...that's also non-sequitur. JS must, of course, appeal in turn to C/C++ so a "browser written in JS" would need privileged APIs provided by C/C++ or something lower level.
What I'm saying is something very direct: there's no other ubiquitous programming language for the web. JS is the only game in town. As a result, when we describe imperative behavior in prose (as the HTML5 spec does) that behavior could, in theory, be implemented in JS (or some sub/super-set). Since HTML, DOM, and CSS aren't Turing-complete, they naturally belong at a "higher level" in the web platform stack.
Now, all of this sounds dangerously academic and perhaps nuts...but consider that we have to expose APIs for nearly all of this stuff. Whenever we add something to HTML, CSS, etc., it always comes with some sort of API. Now, that could be a good API, or it could be an obtuse turn around the parser after some terrible string concatenation.
I'm claiming that you get better APIs when you design your imperative explanation of the declarative stuff -- which you MUST do for specs to be sane -- in JS. This means designing new APIs to help you accomplish the task at hand as you go. Doing it that way ends you up with the types, APIs, and security boundaries you're going to need in the end anyway. Doing it the other way, patching crap onto the side later without explaining how the declarative stuff "works", just leads to the pain and constant need for case-by-case revision that we see in today's web APIs.
That's the whole argument in 4 'grafs. It's subtle, but I hope not terribly controversial. Importantly, nothing about it demands giving up on any of Hixie's 5 arguments. He can keep 'em all and still get a well-layered platform. We've got enough examples of doing it wrong under our belt to see how painful the badly-layered web is today. We can end this insanity -- not by claiming that any part of the platform is "more important" -- by explaining the platform in layers, higher levels in terms of the lower levels.