Tags: declarative

12

sparkline

Thursday, October 4th, 2018

Declaration

I like the robustness that comes with declarative languages. I also like the power that comes with imperative languages. Best of all, I like having the choice.

Take the video and audio elements, for example. If you want, you can embed a video or audio file into a web page using a straightforward declaration in HTML.

<audio src="..." controls><!-- fallback goes here --></audio>

Straightaway, that covers 80%-90% of use cases. But if you need to do more—like, provide your own custom controls—there’s a corresponding API that’s exposed in JavaScript. Using that API, you can do everything that you can do with the HTML element, and a whole lot more besides.

It’s a similar story with animation. CSS provides plenty of animation power, but it’s limited in the events that can trigger the animations. That’s okay. There’s a corresponding JavaScript API that gives you more power. Again, the CSS declarations cover 80%-90% of use cases, but for anyone in that 10%-20%, the web animation API is there to help.

Client-side form validation is another good example. For most us, the HTML attributes—required, type, etc.—are probably enough most of the time.

<input type="email" required />

When we need more fine-grained control, there’s a validation API available in JavaScript (yes, yes, I know that the API itself is problematic, but you get the point).

I really like this design pattern. Cover 80% of the use cases with a declarative solution in HTML, but also provide an imperative alternative in JavaScript that gives more power. HTML5 has plenty of examples of this pattern. But I feel like the history of web standards has a few missed opportunities too.

Geolocation is a good example of an unbalanced feature. If you want to use it, you must use JavaScript. There is no declarative alternative. This doesn’t exist:

<input type="geolocation" />

That’s a shame. Anyone writing a form that asks for the user’s location—in order to submit that information to a server for processing—must write some JavaScript. That’s okay, I guess, but it’s always going to be that bit more fragile and error-prone compared to markup.

(And just in case you’re thinking of the fallback—which would be for the input element to be rendered as though its type value were text—and you think it’s ludicrous to expect users with non-supporting browsers to enter latitude and longitude coordinates by hand, I direct your attention to input type="color": in non-supporting browsers, it’s rendered as input type="text" and users are expected to enter colour values by hand.)

Geolocation is an interesting use case because it only works on HTTPS. There are quite a few JavaScript APIs that quite rightly require a secure context—like service workers—but I can’t think of a single HTML element or attribute that requires HTTPS (although that will soon change if we don’t act to stop plans to create a two-tier web). But that can’t have been the thinking behind geolocation being JavaScript only; when geolocation first shipped, it was available over HTTP connections too.

Anyway, that’s just one example. Like I said, it’s not that I’m in favour of declarative solutions instead of imperative ones; I strongly favour the choice offered by providing declarative solutions as well as imperative ones.

In recent years there’s been a push to expose low-level browser features to developers. They’re inevitably exposed as JavaScript APIs. In most cases, that makes total sense. I can’t really imagine a declarative way of accessing the fetch or cache APIs, for example. But I think we should be careful that it doesn’t become the only way of exposing new browser features. I think that, wherever possible, the design pattern of exposing new features declaratively and imperatively offers the best of the both worlds—ease of use for the simple use cases, and power for the more complex use cases.

Previously, it was up to browser makers to think about these things. But now, with the advent of web components, we developers are gaining that same level of power and responsibility. So if you’re making a web component that you’re hoping other people will also use, maybe it’s worth keeping this design pattern in mind: allow authors to configure the functionality of the component using HTML attributes and JavaScript methods.

Tuesday, June 12th, 2018

Resilient, Declarative, Contextual

This is really good breakdown of what’s different about CSS (compared to other languages).

These differences may feel foreign, but it’s these differences that make CSS so powerful. And it’s my suspicion that developers who embrace these things, and have fully internalized them, tend to be far more proficient in CSS.

Friday, June 8th, 2018

Registering service workers

In chapter two of Going Offline, I talk about registering your service worker wrapped up in some feature detection:

<script>
if (navigator.serviceworker) {
  navigator.serviceworker.register('/serviceworker.js');
}
</script>

But I also make reference to a declarative way of doing this that isn’t very widely supported:

<link rel="serviceworker" href="/serviceworker.js">

No need for feature detection there. Thanks to the liberal error-handling model of HTML (and CSS), browsers will just ignore what they don’t understand, which isn’t the case with JavaScript.

Alas, it looks like that nice declarative alternative isn’t going to be making its way into browsers anytime soon. It has been removed from the HTML spec. That’s a shame. I have a preference for declarative solutions where possible—they’re certainly easier to teach. But in this case, the JavaScript alternative isn’t too onerous.

So if you’re reading Going Offline, when you get to the bit about someday using the rel value, you can cast a wistful gaze into the distance, or shed a tiny tear for what might have been …and then put it out of your mind and carry on reading.

Monday, January 22nd, 2018

Bad Month for the Main Thread - daverupert.com

JavaScript is CPU intensive and the CPU is the bottleneck for performance.

I’m on Team Dave.

But darn it all, I just want to build modular websites using HTML and a little bit of JavaScript.

Monday, October 2nd, 2017

Web Components: The Long Game – Infrequently Noted

One of the things we’d hoped to enable via Web Components was a return to ctrl-r web development. At some level of complexity and scale we all need tools to help cope with code size, application structure, and more. But the tender, loving maintainance of babel and webpack and NPM configurations that represents a huge part of “front end development” today seems…punitive. None of this should be necessary when developing one (or a few) components and composing things shouldn’t be this hard. The sophistication of the tools needs to get back to being proportional with the complexity of the problem at hand.

I completely agree with Alex here. But that’s also why I was surprised and disheartened when I linked to Monica’s excellent introduction to web components that a package manager seemed to be a minimum requirement.

Thursday, September 21st, 2017

Web truths: CSS is not real programming | Christian Heilmann

A lot of “CSS is not real programming” arguments are a basic misunderstanding what CSS is there to achieve. If you want full control over and interface and strive for pixel perfection – don’t use it. If you want to build an interface for an inclusive and diverse web, CSS is a great tool.

Christian does a good job of describing the much-misunderstood declarative nature of CSS.

Also:

In any case, belittling people who write CSS and considering them not real developers is arrogant nonsense.

Thursday, May 18th, 2017

Mavo: A new, approachable way to create Web applications

A really interesting new project from Lea that aims to put dynamic sites within the reach of everyone. The emphasis is on declarative languages—HTML and CSS—no JavaScript knowledge required.

Lea has also written an introductory article on Smashing Mag.

Thursday, April 20th, 2017

There are maps for these territories | Clearleft

A great piece from Danielle on the different mental models needed for different languages. When someone describes a language—like CSS—as “broken”, it may well be that there’s a mismatch in mental models.

CSS isn’t a programming language. It’s a stylesheet language. We shouldn’t expect it to behave like a programming language. It has its own unique landscape and structures, ones that people with programming language mental maps might not expect.

I believe that this mismatch of expectation is what has led to the current explosion of CSS-in-JS solutions. Confronted with a language that seems arbitrary and illogical, and having spent little or no time exposed to the landscape, developers dismiss CSS as ‘broken’ and use systems that either sweep it under the rug, or attempt to force it into alignment with the landscape of a programming language — often sacrificing some of the most powerful features of CSS.

Monday, August 29th, 2016

MarkApp: Building apps with HTML

Here’s an interesting collection from Lea: small JavaScript libraries that do their configuration declaratively via HTML, rather than in JavaScript.

Sunday, June 12th, 2016

Declarative Design Tools | Jon Gold

Jon introduces a new tool with a very interesting observation: up until now, all our graphic design tools have been imperative rather than declarative

With our current tools we’re telling the computer how to design the vision we have in our head (by tapping on our input devices for every element on the screen); in our future tools we will tell our computers what we want to see, and let them figure out how to move elements around to get there.

Friday, November 27th, 2015

HTML5: The New Flash

A new presentation from the wonderfully curmudgeonly Steven Pemberton, the Nosferatu of the web. Ignore the clickbaity title.

I don’t agree with everything he says here, but I strongly agree with his preference for declarative solutions over (or as well as) procedural ones. In short: don’t make JavaScript for something that could be handled in markup.

This part really, really resonated with me:

The web is the way now that we distribute information. We will need the web pages we create now to be readable in 100 years time, just as we can still read 100-year-old books.

Requiring a webpage to depend on a particular 100-year-old implementation of Javascript is not exactly evidence of future-thinking.

Monday, August 5th, 2013

Not Real Programming by John Allsopp

A terrific long-zoom look at web technologies, pointing out that the snobbishness towards declarative languages is a classic example of missing out on the disruptive power of truly innovative ideas …much like the initial dismissive attitude towards the web itself.