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December 7, 2015

Filed under: tech»web

How We're Fast

Over the Thanksgiving holiday, when I wasn't busily digesting as much cornbread stuffing as I could eat, I spent some time running WebPageTest against various projects that the Seattle Times Interactive team has built. The news industry as a whole may not care about speed, but I do, and I want our pages as fast as possible — especially the ones that are embedded in the regular CMS via responsive frames.

After all the testing, I'm generally pleased by how our stuff stacks up, especially when compared against the rest of the site. We have some advantages, of course: our pages typically have fewer ads, and we can strip down the page for maximum efficiency. But it's also the result of a lot of hard work on our news app template, ensuring that every project comes with smart decisions built in. I genuinely think that all news pages could be this fast, so it's worth talking about how we've made it happen, especially for other news organizations that use a similar flat-file approach to their interactives.

Browserify with care

We use Browserify to package up our JavaScript, because we're not savages, and you need some sort of module system for JavaScript these days. Browserify builds all our scripts into a single file, which is important for high-latency connections (which means most cellular networks, even on 4G). We also make sure to load that bundle file with the async attribute at the bottom of the page, so that it won't block rendering.

All of that is pretty standard best practice, but we've also learned that Browserify can be dangerous if you're not careful. A lot of NPM modules are published with the unminified, debug version of the library as the default export from the module. Angular in particular is bad about this: running require("angular") on its own will load a file filled with comments and documentation, totalling more than a megabyte in size (even after gzip, it's still more than 200KB). That's huge!

As a result, one of our production checklist items is to make sure that we are loading the minified version of any external libraries. We also use the browser property in our package.json file to alias common libraries to their minified versions, so that when we require Angular, jQuery, or Leaflet, it automatically defaults to the smallest file.

Gzip on S3

Like a lot of newsroom developers, my team hosts files on Amazon S3, mostly because it's cheap and reliable. People like to think about S3 as though it's just a normal, heirarchical flat-file server, like Apache or Nginx, but it's not. S3 is really a key-value store: you put in a path, and it spits back a prerecorded reply, including the headers.

If you think of S3 as a server, you'll expect it to do a bunch of things that it doesn't actually do. For example, it doesn't set a cache expiration date, and it doesn't know about content types. It also doesn't understand about Gzip compression, so it'll merrily serve your files in their uncompressed form, making them way bigger than they need to be, even if the browser requests the compressed version.

We get around this by running a compression stage on any text-based file during deployment, and setting the headers for the stored object to match. This does mean that theoretically, a browser that doesn't support Gzip will be unable to request that content, because S3 will always respond with compressed content no matter what Accepts-Encoding header the browser sends. Luckily, every browser since IE4 supports it.

Reduce framework code

I love Angular. If you want to quickly generate a visualization with powerful tools for filtering and data binding, you can't do much better. I personally think it's an order of magnitude better than D3. But Angular can also be brutally slow: its change detection algorithm requires a lot of time and memory as a tradeoff for developer convenience.

On a recent project that looked at animal imports, we started with Angular as a way to test out the visualization, but soon noticed that it was taking three or four seconds just to parse and apply the data. On a desktop, that time is a drag. On mobile, it's likely to get the tab terminated, or convince readers that there's something wrong with it.

When the profiler says that you're spending that much time in JavaScript, there are two options. The first is to try to find ways to work around the framework, which can range from unpleasant to actively painful. The second is to just rewrite in vanilla JS. It sounds more difficult to do the rewrite, but if all you're doing is data-binding and events, you can usually replace it pretty easily with a little templating and some custom data attributes. The resulting code isn't as clean or simple, but in the case of the animal imports, it dropped our JS execution time to under 100ms. That's fast.

Even jQuery can be optional these days. Because we compile ES6 down with Babel, a lot of DOM code that would be ungainly can become elegant. Template strings and arrow functions alone have allowed us to cut out DOM libraries entirely, and as a result many of our interactives consist of no external libraries at all. If you haven't checked into the advantages of using Babel in your build process, it's well worth another look.

Reduce third-party code

The number one contributor to page load time is not written by journalists: it's the third-party ad code that runs on the page. There may be only so much you can do about this, since it pays the bills, and of course it may not even apply on embedded graphics. But on our standalone pages, I've taken a strong stance on implementing all code ourselves whenever possible. For example, although our commenting system usually requires multiple scripts loaded synchronously, I wrote a loader that runs through and adds them asynchronously, and only after a user clicks on the "view comments" banner. We can't avoid the hit, but we can delay it until well after the rest of the page has had a chance to render.

Lazy-load everything

Once you've delayed scripts with the async attribute, trimmed the size of those scripts and compressed them, and deferred as much third-party code as you can, what's left over? In our case, this is where we start getting into the structure of the actual interactive, and how it loads itself. For most interactives, we embed data directly into the page, but beyond a certain size it becomes worthwhile to grab it via AJAX instead.

But there's another way to think about lazy-loading, and that's to consider what format you're actually using to populate the page. I'm as big a fan of progressive enhancement as anyone else, but in the case of my team, what we produce is interactive — there's literally no point if JavaScript is disabled. I've found that moving content into JSON and then templating it onto the page can reduce download times significantly, while the speed hit is negligible. Finding the balance between network speed and JavaScript execution time is a constant process for us.

When performance matters

Finally, a note of caution: as much fun as it is to squeeze every last millisecond out of the browser, I'm a little uncomfortable making it the alpha and omega of the job. Ultimately, our goal is to inform people — we'd like that to be fast, but a fast page with bad or misleading reporting is still a failure.

What I like about front-end speed is that it serves as a useful proxy for site quality. A site that's fast can't load too many ads. It can't serve too many tracking scripts. It has to put the reader first. It's easy, much of the time, to chip away at performance in the name of business metrics: loading an additional analytics script to get more information, or an obnoxious ad for a short-term revenue boost.

But if you put speed first, every decision has to start from the perspective of "what's good for the reader?" It's hard to measure the impact of good journalism, but we can have metrics for speed and other technical aspects of the presentation. We can spend more time on the former if we have strong, user-centric guidelines on the latter. If we want people to give us money over the long term, that seems like the only healthy strategy to me.

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