Journal tags: grunt

CSS got some pretty nifty features recently. There’s the min() and max() functions. If you use them for, say, width you can use one rule where previously you would’ve needed to use two (a width declaration followed by either min-width or max-width). But they can also be applied to font-size! That’s very nifty—we’ve never had min-font-size or max-font-size properties.

There’s also the clamp() function. That allows you to set a minimum size, a default size, and a maximum size. Again, it can be used for lengths, like width, or for font-size.

Over on thesession.org, I’ve had some media queries in place for a while now that would increase the font-size for larger screens. It’s nothing crucial, just a nice-to-have so that on wide screens, the font is bumped up accordingly. I realised I could replace all those media queries with one clamp() statement, thanks to the vw (viewport width) unit:

font-size: clamp(1rem, 1.333vw, 1.5rem);

By default, the font-size is 1.333vw (1.333% of the viewport width), but it will never get smaller than 1rem and it will never get larger than 1.5rem.

That works, but there’s a bit of an issue with using raw vw units like that. If someone is on a wide screen and they try to adjust the font size, nothing will happen. The viewport width doesn’t change when you bump the font size up or down.

The solution is to mix in some kind of unit that does respond to the font size being bumped up or down (like, say, the rem unit). Handily, clamp() allows you to combine units, just like calc(). So I can do this:

font-size: clamp(1rem, 0.5rem + 0.666vw, 1.5rem);

The result is much the same as my previous rule, but now—thanks to the presence of that 0.5rem value—the font size responds to being adjusted by the user.

You could use a full 1rem in that default value:

font-size: clamp(1rem, 1rem + 0.333vw, 1.5rem);

…but if you do that, the minimum size (1rem) will never be reached—the default value will always be larger. So in effect it’s no different than saying:

font-size: min(1.rem + 0.333vw, 1.5rem);

I mentioned this to Chris just the other day.

Anyway, I got the result I wanted. I wanted the font size to stay at the browser default size (usually 16 pixels) until the screen was larger than around 1200 pixels. From there, the font size gets gradually bigger, until it hits one and a half times the browser default (which would be 24 pixels if the default size started at 16). I decided to apply it to the :root element (which is html) using percentages:

:root {
  font-size: clamp(100%, 50% + 0.666vw, 150%);
}

(My thinking goes like this: if we take a screen width of 1200 pixels, then 1vw would be 12 pixels: 1200 divided by 100. So for a font size of 16 pixels, that would be 1.333vw. But because I’m combining it with half of the default font size—50% of 16 pixels = 8 pixels—I need to cut the vw value in half as well: 50% of 1.333vw = 0.666vw.)

So I’ve got the CSS rule I want. I dropped it in to the top of my file and…

I got an error.

There was nothing wrong with my CSS. The problem was that I was dropping it into a Sass file (.scss).

Perhaps I am showing my age. Do people even use Sass any more? I hear that post-processors usurped Sass’s dominance (although no-one’s ever been able to explain to me why they’re different to pre-processers like Sass; they both process something you’ve written into something else). Or maybe everyone’s just writing their CSS in JS now. I hear that’s a thing.

The Session is a looooong-term project so I’m very hesitant to use any technology that won’t stand the test of time. When I added Sass into the mix, back in—I think—2012 or so, I wasn’t sure whether it was the right thing to do, from a long-term perspective. But it did offer some useful functionality so I went ahead and used it.

Now, eight years later, it was having a hard time dealing with the new clamp() function. Specifically, it didn’t like the values being calculated through the addition of multiple units. I think it was clashing with Sass’s in-built ability to add units together.

I started to ask myself whether I should still be using Sass. I looked at which features I was using…

Variables. Well, now we’ve got CSS custom properties, which are even more powerful than Sass variables because they can be updated in real time. Sass variables are like const. CSS custom properties are like let.

Mixins. These can be very useful, but now there’s a lot that you can do just in CSS with calc(). The built-in darken() and lighten() mixins are handy though when it comes to colours.

Nesting. I’ve never been a fan. I know it can make the source files look tidier but I find it can sometimes obfuscate what you’re final selectors are going to look like. So this wasn’t something I was using much any way.

Multiple files. Ah! This is the thing I would miss most. Having separate .scss files for separate interface elements is very handy!

But globbing a bunch of separate .scss files into one .css file isn’t really a Sass task. That’s what build tools are for. In fact, that’s what I was already doing with my JavaScript files; I write them as individual .js files that then get concatenated into one .js file using Grunt.

(Yes, this project uses Grunt. I told you I was showing my age. But, you know what? It works. Though seeing as I’m mostly using it for concatenation, I could probably replace it with a makefile. If I’m going to use old technology, I might as well go all the way.)

I swapped out Sass variables for CSS custom properties, mixins for calc(), and removed what little nesting I was doing. Then I stripped the Sass parts out of my Grunt file and replaced them with some concatenation and minification tasks. All of this makes no difference to the actual website, but it means I’ve got one less dependency …and I can use clamp()!

Remember a little while back when I was making a dark mode for my site? I made this observation:

Let’s just take a moment here to pause and reflect on the fact that we can now use CSS to create all sorts of effects that previously required a graphic design tool like Photoshop.

It feels like something similar has happened with tools like Sass. Sass was the hare. CSS is the tortoise. Sass blazed the trail, but now native CSS can achieve much the same result.

It’s like when we used to need something like jQuery to do DOM Scripting succinctly using CSS selectors. Then we got things like querySelector() in JavaScript so we no longer needed the trailblazer.

I’ve said it before and I’ll say it again, the goal of any good library should be to get so successful as to make itself redundant. That is, the ideas and functionality provided by the tool are so useful and widely adopted that the native technologies—HTML, CSS, and JavaScript—take their cue from those tools.

You could argue that this is what happened with Flash. It certainly happened with jQuery and Sass. I’m pretty sure we’ll see the same cycle play out with frameworks like React.

I had some problems with my bouzouki recently. Now, I know my bouzouki pretty well. I can navigate the strings and frets to make music. But this was a problem with the pickup under the saddle of the bouzouki’s bridge. So it wasn’t so much a musical problem as it was an electronics problem. I know nothing about electronics.

I found it incredibly frustrating. Not only did I have no idea how to fix the problem, but I also had no idea of the scope of the problem. Would it take five minutes or five days? Who knows? Not me.

My solution to a problem like this is to pay someone else to fix it. Even then I have to go through the process of having the problem explained to me by someone who understands and cares about electronics much more than me. I nod my head and try my best to look like I’m taking it all in, even though the truth is I have no particular desire to get to grips with the inner workings of pickups—I just want to make some music.

That feeling of frustration I get from having wiring issues with a musical instrument is the same feeling I get whenever something goes awry with my web server. I know just enough about servers to be dangerous. When something goes wrong, I feel very out of my depth, and again, I have no idea how long it will take the fix the problem: minutes, hours, days, or weeks.

I had a very bad day yesterday. I wanted to make a small change to the Clearleft website—one extra line of CSS. But the build process for the website is quite convoluted (and clever), automatically pulling in components from the site’s pattern library. Something somewhere in the pipeline went wrong—I still haven’t figured out what—and for a while there, the Clearleft website was down, thanks to me. (Luckily for me, Danielle saved the day …again. I’d be lost without her.)

I was feeling pretty down after that stressful day. I felt like an idiot for not knowing or understanding the wiring beneath the site.

But, on the other hand, considering I was only trying to edit a little bit of CSS, maybe the problem didn’t lie entirely with me.

There’s a principle underlying the architecture of the World Wide Web called The Rule of Least Power. It somewhat counterintuitively states that you should:

choose the least powerful language suitable for a given purpose.

Perhaps, given the relative simplicity of the task I was trying to accomplish, the plumbing was over-engineered. That complexity wouldn’t matter if I could circumvent it, but without the build process, there’s no way to change the markup, CSS, or JavaScript for the site.

Still, most of the time, the build process isn’t a hindrance, it’s a help: concatenation, minification, linting and all that good stuff. Most of my frustration when something in the wiring goes wrong is because of how it makes me feel …just like with the pickup in my bouzouki, or the server powering my website. It’s not just that I find this stuff hard, but that I also feel like it’s stuff I’m supposed to know, rather than stuff I want to know.

On that note…

Last week, Paul wrote about getting to grips with JavaScript. On the very same day, Brad wrote about his struggle to learn React.

I think it’s really, really, really great when people share their frustrations and struggles like this. It’s very reassuring for anyone else out there who’s feeling similarly frustrated who’s worried that the problem lies with them. Also, this kind of confessional feedback is absolute gold dust for anyone looking to write explanations or documentation for JavaScript or React while battling the curse of knowledge. As Paul says:

The challenge now is to remember the pain and anguish I endured, and bare that in mind when helping others find their own path through the knotted weeds of JavaScript.

After listening to Scott rave on about how much of a perceived-performance benefit he got from inlining critical CSS on first load, I thought I’d give it a shot over at The Session. On the chance that this might be useful for others, I figured I’d document what I did.

The idea here is that you can give a massive boost to the perceived performance of the first page load on a site by putting the most important CSS in the head of the page. Then you cache the full stylesheet. For subsequent visits you only ever use the external stylesheet. So if you’re squeamish at the thought of munging your CSS into your HTML (and that’s a perfectly reasonable reaction), don’t worry—this is a temporary workaround just for initial visits.

My particular technology stack here is using Grunt, Apache, and PHP with Twig templates. But I’m sure you can adapt this for other technology stacks: what’s important here isn’t the technology, it’s the thinking behind it. And anyway, the end user never sees any of those technologies: the end user gets HTML, CSS, and JavaScript. As long as that’s what you’re outputting, the specifics of the technology stack really don’t matter.

Generating the critical CSS

Okay. First question: how do you figure out which CSS is critical and which CSS can be deferred?

To help answer that, and automate the task of generating the critical CSS, Filament Group have made a Grunt task called grunt-criticalcss. I added that to my project and updated my Gruntfile accordingly:

grunt.initConfig({
    // All my existing Grunt configuration goes here.
    criticalcss: {
        dist: {
            options: {
                url: 'http://thesession.dev',
                width: 1024,
                height: 800,
                filename: '/path/to/main.css',
                outputfile: '/path/to/critical.css'
            }
        }
    }
});

I’m giving it the name of my locally-hosted version of the site and some parameters to judge which CSS to prioritise. Those parameters are viewport width and height. Now, that’s not a perfect way of judging which CSS matters most, but it’ll do.

Then I add it to the list of Grunt tasks:

// All my existing Grunt tasks go here.
grunt.loadNpmTasks('grunt-criticalcss');

grunt.registerTask('default', ['sass', etc., 'criticalcss']);

The end result is that I’ve got two CSS files: the full stylesheet (called something like main.css) and a stylesheet that only contains the critical styles (called critical.css).

Cache-busting CSS

Okay, this is a bit of a tangent but trust me, it’s going to be relevant…

Most of the time it’s a very good thing that browsers cache external CSS files. But if you’ve made a change to that CSS file, then that feature becomes a bug: you need some way of telling the browser that the CSS file has been updated. The simplest way to do this is to change the name of the file so that the browser sees it as a whole new asset to be cached.

You could use query strings to do this cache-busting but that has some issues. I use a little bit of Apache rewriting to get a similar effect. I point browsers to CSS files like this:

<link rel="stylesheet" href="/css/main.20150310.css">

Now, there isn’t actually a file named main.20150310.css, it’s just called main.css. To tell the server where the actual file is, I use this rewrite rule:

RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.+).(d+).(js|css)$ $1.$3 [L]

That tells the server to ignore those numbers in JavaScript and CSS file names, but the browser will still interpret it as a new file whenever I update that number. You can do that in a .htaccess file or directly in the Apache configuration.

Right. With that little detour out of the way, let’s get back to the issue of inlining critical CSS.

Differentiating repeat visits

That number that I’m putting into the filenames of my CSS is something I update in my Twig template, like this (although this is really something that a Grunt task could do, I guess):

{% set cssupdate = '20150310' %}

Then I can use it like this:

<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">

I can also use JavaScript to store that number in a cookie called csscached so I’ll know if the user has a cached version of this revision of the stylesheet:

<script>
document.cookie = 'csscached={{ cssupdate }};expires="Tue, 19 Jan 2038 03:14:07 GMT";path=/';
</script>

The absence or presence of that cookie is going to be what determines whether the user gets inlined critical CSS (a first-time visitor, or a visitor with an out-of-date cached stylesheet) or whether the user gets a good ol’ fashioned external stylesheet (a repeat visitor with an up-to-date version of the stylesheet in their cache).

Here are the steps I’m going through:

First of all, set the Twig cssupdate variable to the last revision of the CSS:

{% set cssupdate = '20150310' %}

Next, check to see if there’s a cookie called csscached that matches the value of the latest revision. If there is, great! This is a repeat visitor with an up-to-date cache. Give ‘em the external stylesheet:

{% if _cookie.csscached == cssupdate %}
<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">

If not, then dump the critical CSS straight into the head of the document:

{% else %}
<style>
{% include '/css/critical.css' %}
</style>

Now I still want to load the full stylesheet but I don’t want it to be a blocking request. I can do this using JavaScript. Once again it’s Filament Group to the rescue with their loadCSS script:

 <script>
    // include loadCSS here...
    loadCSS('/css/main.{{ cssupdate }}.css');

While I’m at it, I store the value of cssupdate in the csscached cookie:

    document.cookie = 'csscached={{ cssupdate }};expires="Tue, 19 Jan 2038 03:14:07 GMT";path=/';
</script>

Finally, consider the possibility that JavaScript isn’t available and link to the full CSS file inside a noscript element:

<noscript>
<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">
</noscript>
{% endif %}

And we’re done. Phew!

Here’s how it looks all together in my Twig template:

{% set cssupdate = '20150310' %}
{% if _cookie.csscached == cssupdate %}
<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">
{% else %}
<style>
{% include '/css/critical.css' %}
</style>
<script>
// include loadCSS here...
loadCSS('/css/main.{{ cssupdate }}.css');
document.cookie = 'csscached={{ cssupdate }};expires="Tue, 19 Jan 2038 03:14:07 GMT";path=/';
</script>
<noscript>
<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">
</noscript>
{% endif %}

You can see the production code from The Session in this gist. I’ve tweaked the loadCSS script slightly to match my preferred JavaScript style but otherwise, it’s doing exactly what I’ve outlined here.

The result

According to Google’s PageSpeed Insights, I done good.