Infrequently Noted

Alex Russell on browsers, standards, and the process of progress.

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Class Warfare

And so we're at an impasse.

At the last TC39 meeting, after spending what felt like an eternity on the important topic of UTF-16 encoding, the last day hastily ended with two topics that simply could not be any more urgent: can we get something done about data mutation observation -- the underpinnings for every data binding system worth a damn -- and classes.

As you might imagine, classes got at least one cold shoulder, but this time we were able to suss out the roots of the objection: the latest majority-agreed proposal ("Maximally Minimal Classes") isn't "high water mark" classes and, since so much has been given up to get something moved down the field, classes are no longer worth having. In this post I'll outline a bit of the debate so far, current state, and hopefully convince you that the anti-classicist's arguments are weak.

But first: why classes at all?

There's an ambient argument in the JS world that "we don't need no stinking classes". That all we must do to save the language is teach people the zen of function objects and closures and all will be well with the world...and if we lose some people, so what? I don't want to tar everyone who sympathizes with the beginning of that sentiment with the obvious negatives of the last bit, but that's the overall gist I get. In this view, classes are an unnecessary and lead people to consider JS code the "wrong" way. I've written before about how in ES6 class means function, but that doesn't mollify the discontent.

But then why any language feature at all? Why isn't assembler good enough for everyone? Or C? Or C++?

Turns out the answer is "human frailty". Or put a different way, the process of cognition depends on very limited amounts of short-term stack space in our wetware, and computing languages are about making the computer hospitable for the human, not about telling the system what to do. Our tradeoffs in languages would look much different if we could all easily recall 20 or 30 things at a time instead of 5-10. Languages are tools for freeing creative people from registers and stacks and heaps and memory management and all the rest; all while trying to keep the creative process grounded in the reality that it's memory words in a Von Neumann architecture; without that grounding we'd end up too disconnected from the system to deliver anything practical.

Abstractions, high-level semantics, types...they're all pivots, ways of considering sets of things while working with an individual example of that thing mentally. You don't consider every case all at once and don't remember everything about the system at one time; instead you focus on the arguments to the current function which creates it's own scope. All of these mechanisms create ways of limiting what you need to think about. They ease the burden of associating some things with other things by allowing you to consider smaller cases and allowing you to create or break limitations as they become variously helpful and harmful to getting something done. And we have lots of words to describe the things we find painful about dealing with the overhead of remembering; of a lack of directness and locality: "spaghetti code", "unmaintainable", "badly factored", "tightly coupled", etc. Where there's a new fad in programming, odds are high that it is being touted as a solution to some aggregate behavior which causes a reasonable local decision to become globally sub-optimal. This is what language features are for and why, when you see yourself using the same patterns over and over again, something is deeply wrong.

I'll say this again (and imagine me saying it sloooooowly): languages evolve in response to the pain caused by complexity. The corollary is that language which don't evolve to remove complexity, or which add it in day-to-day usage cause pain. Pain is almost always bad.

Complexity takes many forms, but the process of disambiguation when looking at a syntactic form that relies on a pattern is one of the easiest to take off the table. You'll see this in my work in lots of areas: Web Components make the relationship between markup and eventual behavior less ambiguous when you read the HTML, Shadow DOM creates an isolation boundary for CSS and HTML that make it easier to consider a "thing" in isolation when building and using them, classes in JS make it easier to read some bit of code and not be tripped up by the many meanings of the word function, and many of the features I've advocated for in CSS (mixins, hierarchy, variables) are factoring mechanisms that make it simpler to pivot between repeated stuff and the ad-hoc visual semantics of the document that mean so much to the design language.

Not only should we write off the luddites, we should consider every step towards lower complexity good and steps towards complexity and slower understanding to be bad and actively harmful. Tortured claims about how "you aren't going to need those things" need to be met with evidence; in this case, what do the pervasive libraries in the ecosystem do? Yeah, those are complexity to be taken off the table. The agenda is clear.

But back to classes and JS.

We've been debating various forms of classes in JS since the late '90s. That's right; we've been circling this drain for more than a decade. In that time, nearly every permutation of class system that I'm familiar with has been debated as the rightful heir to the reserved class keyword. From a parallel inheritance structure (non-prototypal) to "just prototypes like we have them today", from "classes as constructor body" to "classes as object literals with constructors", from frozen to gooey and unbaked, from classes as nominal types to totally untyped, we've seen it all. In all of this, the only constant has been failure. TC39 has continued, for more than a decade, to fail to field any class syntax (yes, I have my slice of blame-cake right here). In that time, JS has gone from being important to being critical to the construction of large systems; both on the client and the server. As this has happened, we've seen function pressed into service not only as lambda and method, but module, class, and pretty much every other form of ad-hoc composition system that's needed at any point. We're overdue for adding language-level support for all of these things. The committee has shown great ability to extend and expand upon idioms already in the language, taking syntax as a starting point and using it create new room for reducing pain (the spread operator and destructuring are great examples). Yet still many on the committee, notably Luke Hoban of Microsoft and Waldemar Horwat of Google, worry that a form of class in ES6 that doesn't make coffee for you while also shooting rainbows out of it's behind won't be worth the syntactic space it takes up. I would have worried about this too back in '08 when I first attended a TC39 meeting, but no longer. This is a group that is good at incremental change. Rainbow-shooting technology takes a while to build; meanwhile, wouldn't it be great if we could get a cup of joe around here? We've waited long enough to get something meaningful to build on and with. I want a hell of a lot more than what the Maximally Minimal Classes proposal adds, but they're a starting point, and there will be more ES versions.

So that's Argument #1: people will hate us if class doesn't do enough.

True, perhaps, but they will hate us anyway. Add classes and Mikeal Rogers personally organizes the pitchfork and torch distribution points and leads the march. Don't add classes and the world at large thinks of JS as a joke and a toy -- where'd that giant library/transpiler get to, anyway? You need something after all. Add them and Mikeal can keep not using classes to his heart's content, and if we add classes in the style I prefer (and which Max/Min Classes embody), he can use them as old-skool functions and never care how they were declared; all the while making JS more productive for folks who don't want to buy into a whole lifestyle to get a job done.

What's Argument #2? That instances created from classes aren't frozen. That is to say, it's still possible to add new properties to them later. You know, like every other JS object.

If you're thinking "yes, but isn't there Object.freeze() already?", you're not alone. What you're witnessing here is a debate about what's considered good, not what's possible. You can manually freeze/seal objects to your heart's content, but what the (tiny) minority that is strenuously making argument #2 is demanding is that nobody be allowed to use the word class to create a constructor function body unless the resulting object is automatically frozen. They are willing to hold up the entire train until this preference is mollifed, and are unhappy with any short syntax which does not bless their preferred style.

In fairness, I also would be grumpy to see things go a direction I don't prefer, but consider the following syntaxes that could be deployed in a future version to create frozen classes, none of which are precluded by the Max/Min proposal:

// "const" causes instances to have their properties
// frozen on exiting the constructor
const class Point {
  constructor() { ... }

// Declaring a const properties member causes the // constructor to check for those only, freezing exiting // the constructor class Point { constructor() { ... } const properties { // Object literal ... } }

And I'm sure you can think of a couple of others. The essential distinguishing feature, and the thing that is holding the entire train up, is that the word class without any embellishment whatsoever doesn't work this way. Yes, I know it sounds crazy, but that's where we're at. You can help, though. Erik Arvidsson has implemented Max/Min classes in Traceur and you can try it out in the live repl. If you like/hate it, won't you please let the es-discuss mailing list know? Or just post in the comments here for posterity. We know that these classes need many more features, but your thoughts about this syntax as a starting point couldn't be more timely.

Hoisted From The Comments

Some stuff is too good to leave in the shadows. On my Bedrock post, James Hatfield writes in with a chilling point, but one which I've been making for a long while:

”every year we’re throwing more and more JS on top of the web”

The way things are going in my world, we are looking at replacing the web with JS, not simply layering. At a certain point you look at it all and say “why bother”. Browsers render the DOM not markup. They parse markup. Just cut out the middle man and send out DOM – in the form of JS constructs.

The second part is to stop generating this markup which then must be parsed on a server at the other end of a slow and high latency prone communication channel. Instead send small compact instructions to the browser/client that tells it how to render and when to render. Later you send over the data, when it’s needed...

This is a clear distillation of what scares me about the road we're headed down because for each layer you throw out and decide to re-build in JS, you end up only doing what you must, and that's often a deadline-driven must. Accessibility went to hell? Latency isn't great? Doesn't work at all without script? Can't be searched? When you use built-ins, those things are more-or-less taken care of. When we make them optional by seizing the reigns with script, not only do we wind up playing them off against each other (which matters more, a11y or latency?) we often find that developers ignore the bits that aren't flashy. Think a11y on the web isn't great now? Just wait 'till it's all JS driven.

It doesn't have to be this way. When we get Model Driven Views into the browser we'll have the powerful "just send data and template it on the client side" system everyone's looking for but without threatening the searchability, a11y, and fallback behaviors that make the web so great. And this is indicative of a particularly strong property of markup: it's about relationships. "This thing references that thing over there and does something with it" is hard for a search engine to tease out if it's hidden in code, but if you put it in markup, well, you've got a future web that continues to be great for users, the current crop of developers, and whoever builds and uses systems constructed on top of it all later. That last group, BTW, is you if you use a search engine.

But it wasn't all clarity and light in the comments. Austin Cheney commented on the last post to say:

This article seems to misunderstand the intention of these technologies. HTML is a data structure and nothing more. JavaScript is an interpreted language whose interpreter is supplied with many of the most common HTML parsers. That is as deep as that relationship goes and has little or nothing to do with DOM.

...It would be safe to say that DOM was created because of JavaScript, but standard DOM has little or nothing to do with JavaScript explicitly. Since the release of standard DOM it can be said that DOM is the primary means by which XML/HTML is parsed suggesting an intention to serve as a parse model more than a JavaScript helper.

Types in DOM have little or nothing to do with types in JavaScript. There is absolutely no relationship here and there shouldn’t be...You cannot claim to understand the design intentions around DOM without experience working on either parsers or schema language design, but its operation and design have little or nothing to do with JavaScript. JavaScript is just an interconnecting technology like Java and this is specifically addressed in the specification in Appendix G and H respectively.

And, after I tried to make the case that noting how it is today is no replacement for a vision for how it should be, Austin responds:

The problem with today’s web is that it is so focused on empowering the people that it is forgetting the technology along the way. One school of thought suggests the people would be better empowered if their world were less abstract, cost radically less to build and maintain, and is generally more expressive. One way to achieve such objectives is alter where costs exist in the current software life cycle of the web. If, for instance, the majority of costs were moved from maintenance to initial build then it could be argued that more time is spent being creative instead of maintaining.

I have found that when working in HTML alone that I save incredible amounts of time when I develop only in XHTML 1.1, because the browser tells you where your errors are. ... Challenges are removed and costs are reduced by pushing the largest cost challenges to the front of development.

... The typical wisdom is that people need to be empowered. If you would not think this way in your strategic software planning then why would it make sense to think this way about strategic application of web technologies? ...

This might all sound very rational on one level, but a few points need to be made:

I think Austin's point about moving costs from maintenance to build is supposed to suggest that if we were only more strict about things, we'd have less expensive maintenance of systems, but it's not clear to me that this has anything to do with strictness. My observation from building systems is that this has a lot more to do with being able to build modular, isolated systems that compose well. Combine that with systems that let you iterate fast, and you can grow very large things that can evolve in response to user needs without turning into spaghetti quite so quickly. Yes, the web isn't great for that today, but strictness is orthogonal. Nothing about Web Components demands strictness to make maintainability infinitely better.

And the last point isn't news. Postel's Law isn't a plea about what you, dear software designer, should be doing, it's an insightful clue into the economics of systems at scale. XML tried being strict and it didn't work. Not even for RSS. Mark Pilgrim's famously heroic attempts at building a reliable feed parser match the war stories I've heard out of the builders of every large RSS system I've ever talked to. It's not that it's a nice idea to be forgiving about what you accept, it's that there's no way around it if you want scale. What Austin has done is the classic bait-and-switch: he has rhetorically substituted what works in his organization (and works well!) for what's good for the whole world, or even what's plausible. I see this common logical error in many a standards adherent/advocate. They imagine some world in which it's possible to be strict about what you accept. I think that world might be possible, but the population would need to be less than the size of a small city. Such a population would never have ever created any of the technology we have, and real-world laws would be how we'd adjudicate disputes. As soon as your systems and contracts deal with orders of magnitude more people, it pays to be reliable. You'll win if you do and lose if you don't. It's inescapable. So lets banish this sort of small-town thinking to the mental backwaters where it belongs and get on with building things for everyone. After all, this is about people. Helping sentient beings achieve their goals in ways that are both plausible and effective.

If helping people is not what this is about, I want out.

For Dave and David

Dave Herman jokingly accused me a couple of TC39 meetings ago of being an "advocate for JavaScript as we have it today", and while he meant it in jest, I guess to an extent it's true -- I'm certainly not interested in solutions to problems I can't observe in the wild. That tends to scope my thinking aggressively towards solutions that look like they'll have good adoption characteristics. Fix things that are broken for real people in ways they can understand how to use.

This is why I get so exercised about WebIDL and the way it breaks the mental model of JS's "it's just extensible objects and callable functions". It's also why my discussions with folks at last year's TPAC were so bleakly depressing. I've been meaning to write about TPAC ever since it happened, but the time and context never presented themselves. Now that I got some of my words out about layering in the platform, the time seems right.

Let me start by trying to present the argument I heard from multiple sources, most likely from (in my feeble memory) Anne van Kestern Jonas Sicking(?):

ECMAScript is not fully self-describing. Chapter 8 drives a hole right through the semantics, allowing host objects to whatever they want and more to the point, there's no way in JS to describe e.g. list accessor semantics. You can't subclass an Array in JS meaningfully. JS doesn't follow it's own rules, so why should we? DOM is just host objects and all of DOM, therefore, is Chapter 8 territory.

Brain asploded.

Consider the disconnect: they're not saying "oh, it sure would be nice if our types played better with JS", they're saying "you and what army are gonna make us?" Remember, WebIDL isn't just a shorthand for describing JavaScript classes, it's an entirely parallel type hierarchy.

Many of the Chapter 8 properties and operations are still in the realm of magic from JS today, and we're working to open more of them up over time by giving them API -- in particular I'm hopeful about Allen Wirfs-Brock's work on making array accessors something that we can treat as a protocol -- but it's magic that DOM is appealing to and even specifying itself in terms of. Put this in the back of your brain: DOM's authors have declared that they can and will do magic.

Ok, that's regrettable, but you can sort of understand where it comes from. Browsers are largely C/C++ enterprises and DOM started in most of the successful runtimes as an FFI call from JS to an underlying set of objects which are owned by C/C++. The truth of the document's state was not owned by the JS heap, meaning every API you expose is a conversation with a C++ object, not a call into a fellow JS traveler, and this has profound implications. While we have one type for strings in JS, your C++ side might have bstr, cstring, wstring, std::string, and/or some variant of string16.

JS, likewise, has Number while C++ has char, short int, int, long int, float, double, long double, long long get the idea. If you've got storage, C++ has about 12 names for it. Don't even get me started on Array.

It's natural, then, for DOM to just make up it's own types so long as its raison d'être is to front for C++ and not to be a standard library for JS. Not because it's malicious, but because that's just what one does in C++. Can't count on a particular platform/endianness/compiler/stdlib? Macro that baby into submission. WTF, indeed.

This is the same dynamic that gives rise to the tussle over constructable constructors. To recap, there is no way in JS to create a function which cannot have new on the left-hand-side. Yes, that might return something other than an instance of the function-object on the right-hand side. It might even throw an exception or do something entirely non-sensical, but because function is a JavaScript concept and because all JS classes are just functions, the idea of an unconstructable constructor is entirely alien. It's not that you shouldn't do it...the moment to have an opinion about that particular question never arises in JS. That's not true if you're using magic to front for a C/C++ object graph, though. You can have that moment of introspection, and you can choose to say "no, JS is wrong". And they do, over and over.

What we're witnessing here isn't "right" or "wrong"-ness. It's entirely conflicting world views that wind up in tension because from the perspective of some implementations and all spec authors, the world looks like this:

Not to go all Jeff Foxworthy on you, but if this looks reasonable to you, you might be a browser developer. In this worldview, JS is just a growth protruding from the side of an otherwise healthy platform. But that's not how webdevs think of it. True or not, this is the mental model of someone scripting the browser:

The parser, DOM, and rendering system are browser-provided, but they're just JS libraries in some sense. With <canvas>'s 2D and 3D contexts, we're even punching all the way up to the rendering stack with JS, and it gets ever-more awkward the more our implementations look like the first diagram and not the second.

To get from parser to DOM in the layered world, you have to describe your objects as JS objects. This is the disconnect. Today's spec hackers don't think of their task as the work of describing the imperative bits of the platform in the platform's imperative language. Instead, their mental model (when it includes JS at all) pushes it to the side as a mere consumer in an ecosystem that it is not a coherent part of. No wonder they're unwilling to deploy the magic they hold dear to help get to better platform layering; it's just not something that would ever occur to them.

Luckily, at least on the implementation side, this is changing. Mozilla's work on dom.js is but one of several projects looking to move the source of truth for the rendering system out of the C++ heap and into the JS heap. Practice is moving on. It's time for us to get our ritual lined up with the new reality.

Which brings me too David Flanagan who last fall asked to read my manifesto on how the platform should be structured. Here it is, then:

The network is our bottleneck and markup is our lingua-franca. To deny these facts is to design for failure. Because the network is our bottleneck, there is incredible power in growing the platform to cover our common use cases. To the extent possible, we should attempt to grow the platform through markup first, since markup provides the most value to the largest set of people and provides a coherent way to expose APIs via DOM.

Markup begets JS objects via a parser. DOM, therefore, is merely the largest built-in JS library.

Any place where you cannot draw a line from browser-provided behavior from a tag to the JS API which describes it is magical. The job of Web API designers is first to introduce new power through markup and second to banish magic, replacing it with understanding. There may continue to be things which exist outside of our understanding, but that is a challenge to be met by cataloging and describing them in our language, not an excuse for why we cannot or should not.

The ground below our feet is moving and alignment throughout the platform, while not inevitable, is clearly desirable and absolutely doable in a portable and interoperable way. Time, then, to start making Chapter 8 excuses in the service of being more idiomatic and better layered. Not less and worse.


Jetlag has me in its throes which is as good an excuse as any to share what has been keeping me up many nights over the past couple of years; a theory of the web as a platform.

I had a chance last week to share some of my thinking here to an unlikely audience at EclipseCon, a wonderful experience for which my thanks go to Mike Milinkovich and Ian Skerrett for being crazy enough to invite a "web guy" to give a talk.

One of the points I tried (and perhaps failed) to make in the talk was that in every platform that's truly a platform it's important to have a stable conceptual model of what's "down there". For Java that's not the language, it's the JVM. For the Yes, it bottoms out at C/C++, but that's mostly observable through spooky action at a distance. The expressive capacity of C/C++ show up as limitations and mismatches in web specs all the time, but the essential semantics -- C/C++ is just words in memory that you can do whatever you please with -- are safely hidden away behind APIs and declarative forms that are unfailingly high-level. Until they aren't. And you can forget about composition most of the time.

For a flavor of this, I always turn back to Joel Webber's question to me several years ago: why can't I over-ride the rendering of a border around an HTML element?

It's a fair question and one I wrote off too quickly the first time he posed it. We have <canvas> which lets us draw lines however we like, so why can't we override the path painting for borders? Why isn't it just a method you implement like in Flex or Silverlight?

Put another way: there are some low level APIs in the web that suggest that such power should be in the hands of us mortals. When using a low-level thing, you pay-as-you-go since lower-level things need more code (latency and complexity)...but that's a choice. Today's web is often mysteriously devoid of the sort of sane layering, forcing you to re-build parallel systems to what's already in the browser to get a job done. You can't just subclass the right thing or plug into the right lifecycle method most of the time. Want a <canvas>? Fine. There you go. Want a <span>? Hot <span>s coming up! But don't go getting any big ideas about using the drawing APIs from <canvas> to render your <span>. Both are magic in their own right and for no reason other than that's the way it has always been.

The craziest part in all of this is that JavaScript does exist in the web so you can strictly speaking do whatever you want. Goodness knows that when the platform fails us today, we're all-too-willing to just throw JS at it. It's crazy, in this context then, that spec authors seem to be trying to uphold a golden principle: JavaScript doesn't exist. Writing it out of the story allows you to just claim that your bit of the system is magic and that it doesn't need an exposed lifecycle and plug-in architecture. New things can just be bolted onto the magic, no layering required. It's magical turtles all the way down.

You can see why people who think in terms of VM's and machine words might find this a bit ahem limiting.

But how much should we "web people" care about what they think? After all, "real programmers" have been predicting the imminent death of this toy browser thing for so long that I'm forgetting exactly when the hate took its various turns through the 7 stages; "Applets will save us from this insanity!"..."Ajax is a hack"..."just put a compiler in front of it and treat it as the dumbest assembler ever" (which is at least acceptance, of a sort). The web continues to succeed in spite of all of of this. So why bother with the gnashing of teeth?

Thanks to Steve Souders, I have an answer: every year we're throwing more and more JS on top of the web, dooming our best intended semantic thoughts to suffocation in the Turing tar pit. Inexorably, and until we find a way to send less code down the wire, us is them, and more so every day.

Let that picture sink in: at 180KB of JS on average, script isn't some helper that gives meaning to pages in the breech, it is the meaning of the page. Dress it up all you like, but that's where this is going.

Don't think 180KB of JS is a lot? Remember, that's transfer size which accounts for gzipping, not total JS size. Oy. And in most cases that's more than 3x the size of the HTML being served (both for the page and for whatever iframes it embeds). And that's not all; it's worse for many sites which should know better. Check out those loading "filmstrip" views for gawker, techcrunch, and the NYT. You might be scrolling down, looking at the graphs, and thinking to yourself "looks like Flash is the big ticket item...", and while that's true in absolute terms, Flash isn't what's blocking page loads. JS is.

And what for? What's all that code doing, anyway?

It's there for three reasons: first, to clean up the messes that browser vendors aren't willing or able to clean up for themselves; second, to provide an API that becomes the new platform, and lastly to provide the app-specific stuff you are trying to get across. Only the last one is strictly valuable. You're not including JQuery, Backbone, Prototype or Dojo into your pages just because you like the API (if you are, stop it). You're doing it because the combination of API and even behavior across browsers makes them the bedrock. They are the new lisp of application construction; the common language upon which you and your small team can agree; just don't expect anyone else to be able to pick up your variant without squinting hard.

This is as untenable as it is dangerous. It was this realization that set me and Dimitri Glazkov off to build a team to do something about it more than a year and a half ago. The results are showing up now in the form of Web Components and Shadow DOM, Mutation Observers as plumbing for Model Driven View, and a host of new CSS capabilities and JavaScript language expressiveness wins. If that sounds like a huge pile of seemingly un-related work, let me walk back to one of the motivating questions and then I'll fast forward to the approach:

What would it mean to be able to subclass an HTML Element?

We observed that most of what the current libraries and frameworks are doing is just trying to create their own "widgets" and that most of these new UI controls had a semantic they'd like to describe in a pretty high-level way, an implementation for drawing the current state, and the need to parent other widgets or live in a hierarchy of widgets.

Heeeeeyyyyyy....wait a minute...that sounds a lot like what HTML does! And you even have HTML controls which generate extra elements for visual styling but which you can't access from script. This, BTW, is what you want when building your own controls. Think the bullets of list items or the sliders generated by <input type="range">. There are even these handy (non-constructable!?!) constructors for the superclasses in JS already.

So what would you need access to in order to plug into that existing system? And how should it be described? This, by the way, is the danger zone. Right about this point in the logical chain most folks tend to fall back to what they know best: C++ hacker? Give 'em a crappy C++-inspired high-level-ish JS API that will make the people yelling loudest stop beating you up. Declarative guy? Force everyone to describe their components as separate documents and...yeah. XUL. You get the idea. JavaScript person? Demand the lowest level API and as much unwarranted power as possible and pretend you don't need the browser. JS libraries are the "fuck it, we'll do it live!" of the web.

None of these are satisfying. Certainly not if what we want is a platform of the sort you might consider using "naked". And if your "platform" always needs the same shims here and polyfills there, let me be candid: it ain't no platform. It's some timber and bolts out of which you can make a nice weekend DIY project of building a real platform.

So we need to do better.

What does better look like?

Better is layered. Better is being able to just replace what you need, to plug in your own bits to a whole that supports that instead of making you re-create everything above any layer you want to shim something into. This is why mutable root prototypes in JS and object mutability in general are such cherished and loathed properties of the web. It is great power. It's just a pity we need it so often. Any plan for making things better that's predicated on telling people "oh, just go pile more of your own parallel systems on top of a platform that already does 90% of what you need but which won't open up the API for it" is DOOMED.

Thus began a archaeology project, one which has differed in scope and approach from most of the recently added web capabilities I can think of, not because it's high-level or low-level, but because it is layered. New high-level capabilities are added, but instead of then poking a hole nearly all the way down to C++ when we want a low-level thing, the approach is to look at the high-level thing and say:

How would we describe what it's doing at the next level down in an API that we could expose?

This is the reason low-level-only API proposals drive me nuts. New stuff in the platform tends to be driven by scenarios. You want to do a thing, that thing probably has some UI (probably browser provided), and might invoke something security sensitive. If you start designing at the lowest level, throwing a C++ API over the wall, you've turned off any opportunity or incentive to layer well. Just tell everyone to use the very fine JS API, after all. Why should anyone want more? (hint: graph above). Instead of opening doors, though, it's mostly burden. Everything you have to do from script is expensive and slow and prone to all sorts of visual and accessibility problems by default. If the browser can provide common UI and interaction for the scenario, isn't that better most of the time? Just imagine how much easier it would be to build an app if the initial cut at location information had been <input type="location"> instead of the Geolocation API we have now. True, that input element would need lots of configuration flags and, eventually, a fine-grained API...if only there were a way to put an API onto an HTML element type...hrm...

In contrast, if we go declarative-only we get a lot of the web platform today. Fine at first but horrible to work with over time, prone to attracting API barnacles to fill perceived gaps, and never quite enough. The need for that API keeps coming back to haunt us. We're gonna need both sides, markup and imperative, sooner or later. A framework for thinking about what that might look like seems in order. Our adventure in excavation with Web Components has largely been a success, not because we're looking to "kernalize the browser" in JS -- good or bad, that's an idea with serious reality-hostile properties as soon as you add a network -- but because when you force yourself to think about what's already down there as an API designer, you start making connections, finding the bits that are latent in the platform and should be used to explain more of the high level things in terms of fewer, more powerful primitives at the next layer down. This isn't a manifesto for writing the whole world in JS; it's a reasonable and practical approach for how to succeed by starting high and working backwards from the 80% use-case to something that eventually has most of the flexibility and power that high-end users crave.

The concrete steps are:

  1. Introduce new platform capabilities with high-level, declarative forms. I.e., invent new tags and attributes. DOM gives you an API for free when you do it that way. Everyone's a winner.
  2. When the thing you want feels like something that's already "down there" somewhere, try to explain the bits that already exist in markup in terms of a lower-level JS or markup primitive. If you can't do that or you think your new API has no connection to markup, go back to step 1 and start again.
  3. When it feels like you're inventing new language primitives in DOM just to get around JS language limitations, extend the language, not the API

On the web, JavaScript is what's down there. When it's not, we're doing it wrong. It has taken me a very long time to understand why the Java community puts such a high premium on the "pure java" label, and fundamentally what it says to others in the community is "I appealed to no gods and no magic in the construction of this, merely physics". That's a Good Thing (TM), and the sort of property that proper platforms should embody to the greatest extent possible.

And this brings me to my final point. C/C++ might be what's "down there" for web browsers, but that's also been true of Java. What separates the web and Java, however, is that the Java community sees their imperative abstraction that keeps them from having to think about memory correctness (the JVM) as an asset and many "web people" think of JS as pure liability. I argue that because of the "you're gonna need both sides" dynamic, trying to write JS out of the picture is a dumb as it is doomed to fail. JavaScript is what's "down there" for the web. The web has an imperative backbone and we're never going to expose C/C++ ABI for it, which means JS is our imperative successor. The archaeological dig which is adding features like Web Components is providing more power to JS by the day and if we do this right and describe each bit as a layer with an API that the one above builds on, we can see pretty clearly how the logical regress of the "you must use JS to implement the whole browser" isn't insane. JS itself is implemented as C/C++, so there's always room for the mother tongue and of course many of the APIs that we interact with from JS must be C/C++; you can't write it out of the story -- but that doesn't mean we need to design our APIs there or throw bad design decisions over the wall for someone else to clean up. It is high time we started designing low-level stuff for the web in idiomatic JS (not IDL), start describing the various plug-in points for what they are. We can provide power from our imperative abstraction to and through our declarative layer in ways that make both high and low-level users of the web platform more able to interoperate, build on each other's work, and deliver better experiences at reasonable cost. That's the difference between a minefield and a platform. Only one of them is reasonable to build on.

The trash truck just came by which means it's 6AM here in almost-sunny London. WordPress is likewise telling me that I'm dangerously out of column-inches, so I guess I'll see if I can't get a last hour or two of sleep before the weekend is truly over. The arguments here may not be well presented, and they are subtle, but layering matters. We don't have enough of it and when done well, it can be a powerful tool in ending the battle between imperative and declarative. I'll make the case some other time for why custom element names are a good idea, but consider it in the layered context: if I could subclass HTMLElement from JavaScript in the natural way, why can't I just put a new tag name in the map the parser is using to create instances of all the other element types? Aside from the agreement about the names, what makes the built-in elements so special, anyway?

Cognitive dissonance, ahoy! You're welcome ;-)

Note: this post has evolved in the several days since its initial posting, thanks largely to feedback from Annie Sullivan and Steve Souders. But it's not their fault. I promise.

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