Bootstrap verbosity and mysterious IE problems

Submitted by sonniesedge on Tue, 09/09/2014 - 11:00
Bootstrap? Verbose? Pull the other one. It has bells on it.

Nobody can deny it. Bootstrap is bloated. There's a good reason for that - it's the jack-of-all-trades, the swiss army knife, the (not so) little framework that could. If you want it to do something, then it probably can.

The downside of this is that sometimes you experience mysterious problems...

The problem

When we got reports from our QA testers of various form elements randomly missing a border, padding or margins I wasn't too fussed. Maybe a junior had committed bad code, or the caches on our servers were playing up.

However, my heart sank when I heard "it only happens in IE".

The five worst words that a web developer can hear.

I reluctantly fired up an IE VM, stared at the limited IE devtools and saw that the selectors and rules that should be there, just weren't there.


So I checked the CSS files directly to make sure the rules were there.

They were.

Okay. Check that the CSS file I've just checked was actually being loaded.

Yup, it was.

This is the kind of scenario that can make you reach for the gin or a shotgun.

It was only when I realised that the rules that were being ignored all resided at the end of the stylesheet that I realised that I wasn't being gaslit by IE.

I was in fact a victim of the mysterious 4096 selector limit rule in IE10 and below: In any one stylesheet IE will only parse the first 4096 selectors before giving up and, this is important, silently failing.

As always IE, you are so helpful.

But WHY?

But why was it happening? For that I turned to grunt-stylestats and Katie Fenn's Parker, both of which will run through your CSS and gather stats as they go. The key one we needed here is selectors.

Turns out that this isn't entirely Bootstrap's fault. I was being a bit too zealous in my attempts to get all Sass generated by the frontend devs into one CSS file. In particular, I was compiling in the Sass for Font Awesome into our main stylesheet, which was what was taking us over the edge in selector count.

Nuke it from orbit

So how do we get around that? I initially turned to a system called Bless, which will parse your CSS and split it at 4096 selectors, @importing the extra selectors automatically. There was even a nice Grunt plugin for it. It runs at build-time and does what it needs to do quickly and intelligently.

However, a week after doing that I slapped myself, as the more obvious answer was to just take the bulky code - Font Awesome - out of our main stylesheet and move it to its own. Whoop, selector count instantly drops by over a thousand. It's still a blocking CSS resource (a constant problem on that particular site), but at least we get pages rendering consistently in IE.

So, Bootstrap is off the hook here. But only just. Looking at the standard distributed bootstrap.css file with style-stats reveals that there are 2290 selectors in there. That's still 1806 off the IE limit, but it's still ENORMOUS.

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