Sep 22 2014

Dynamic CSS Manipulation with JavaScript

Published by at 1:58 pm under Technology   

Last week I attended the Manning’s Powered By JavaScript one-day conference, the day before Strange Loop. Here are some thoughts on the “Powered By” conference as a whole and on one talk:

Dump Less and SASS: Dynamic CSS Manipulation with JavaScript
Speaker: Michael Mikowski

I wrote recently about CSS, so this talk caught my attention more than any other that day.

Powered By JavaScript Mini-Review

Overall this mini-one-day conference was well executed:

  1. Interesting speakers
  2. Good venue
  3. Very convenient to attend the day before Strange Loop

But I would like to call out a few opportunities to improve:

  1. The registration process was slow, and understaffed. The team running the conference should be able to look at the number of attendees and staff the registration process based on it.
  2. The registration process included registration for speakers in the same line as attendees. As a result, when a speaker reached the front of the line there was a long diversion while the staff was excited to greet and visit with the speaker. That is a wonderful way to treat speakers; but they should be diverted out of the way of the hundreds of people standing in line behind them to just pick up a badge.
  3. This one-day conference was co-located with Strange Loop, so the planners should expect a lot of Strange Loop people there – and plan for students at roughly the same skill level. Unfortunately the JavaScript event was targeted toward less sophisticated developers than typically attend Strange Loop.
  4. Please watch the clock. Many of the speakers did not end at the appointed time.

That sounds too negative. This was a very good effort from Manning, and I recommend attending future Manning JavaScript events.

Diversion #1: The Book

The speaker Michael Mikowski is the co-author, with another speaker at this conference (Josh Powell), of the book “Single Page Web Applications: JavaScript end-to-end”. Based on what I heard at the conference, this book is a little behind the times compared with today’s toolsets. I don’t believe it mentions the current competitive tools out there like Ember, AngularJS, React, and so on. Rather it seems to be about good practices for using an older generation of tools. Still, this was a distraction, because the speaker was fantastic!

Diversion #2: The Speaker

I had not met or seen a talk by Mike Mikowski, but from a look at his website he is a sharp fellow with very interesting things to say. In particular, I wish I had been at his “Fog of SPA” talk; the slides are worth reading, and I wish there was a video to watch, those slides were probably backed up by great stories. (I don’t necessarily agree with every idea in it, though. For example, I find it usually is worth having a build process to use higher level tools.)

This Talk: Dynamic CSS Manipulation with JavaScript

To summarize briefly, the message of this talk was that writing Javascript to emit CSS can replace LESS, Sass, and other CSS tools. Instead of adding another language and server-side build process (for Sass or LESS) to address weaknesses in CSS, you can write JavaScript code which emits CSS, and run that JavaScript code on page load or when needed. There are several important bits to get right to make this performant, for example the CSS for a page should be swapped out all at once to avoid the browser repeatedly re-rendering.

I don’t recall if the talk was recorded on video, but if it appears online, watch it.

As is my (unfortunate?) custom, I will first review a couple of nitpicks:

  • The title of the talk was mis-capitalized as “Dump Less and SASS”, which gets the name of Sass wrong. (Until earlier in 2014, Less was called LESS, incidentally.)
  • I waited anxiously for a glorious revelation in which code that would appear on the slides. Unfortunately, code never appeared. Mike convinced me to consider this idea in the first few minutes. I was ready to look. Please show me code!

Now on to the good stuff. Mike’s idea is interesting and appealing, and perhaps compelling for certain types of web applications. Clearly for the application Mike and friends are building at Qualaroo, it is an ideal and very slick application of technology. Particular appealing ideas:

CSS responsiveness by means of media queries can only respond to the narrow-ish set of information available to a media query. This JavaScript CSS approach can respond to any information at all available to the page, including (for example) the current zoom level.

LESS and Sass offer a good set of abstractions, a big improvement over vanilla CSS. But they only offer what is in their respective boxes. With a JavaScript CSS approach, as a developer you can create whatever specific set of abstractions is valuable for the problem at hand in a specific application.

The JavaScript CSS approach does not need a server-side build process, because it simply runs a little bit of JavaScript in the browser on page load.

The JavaScript CSS approach reduces the number of HTTP requests to load content; the CSS arrives (in a “compressed” form, in the sense that JavaScript to write the specific CSS is probably smaller than that CSS) as part of the JavaScript request.

If you generate CSS programmatically, you don’t have to stop at JavaScript. You can use CoffeeScript to generate JavaScript which generates your CSS, for example.

Actual Code!

Fortunately, while this talk did not include code, there are plenty of other people online doing something vaguely similar, who do publish code. Here are some I found. It is great to see this approach is already out there is common use, not a proprietary invention!

http://www.responsivejs.com/

http://absurdjs.com/

The following are also similar, but for Clojure. There are numerous ways to write your CSS in a different language (JS or otherwise), which already have variables and subroutines and other useful features.

https://github.com/paraseba/cssgen

https://github.com/rathwell/clj-style

https://github.com/noprompt/garden

If you found this post useful, please link to it from your web site, mention it online, or mention it to a colleague.

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