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Fantastic front end performance, part 3 - Big performance wins by serving fonts smarter - A Node.js holiday season, part 8

In Persona we cut our page load times in half by serving fonts smarter. This post outlines exactly how we implemented these performance wins, and gives you tools to do the same.

Introducing connect-fonts

connect-fonts is a Connect font-management middleware that improves @font-face performance by serving locale-specific subsetted font files, reducing downloaded font size up to 80%. It also generates locale/browser-specific @font-face CSS, and manages the CORS header required by Firefox and IE 9+. Subsetted fonts are served from a font pack--a directory tree of font subsets, plus a simple JSON config file. Some common open-source fonts are available in pregenerated font packs on npm, and creating your own font packs is straightforward.

(Feeling lost? We've [put together}(https://gist.github.com/6a68/5187976) a few references to good @font-face resources on the web.)

Static vs dynamic font loading

When you are just serving one big font to all your users, there's not much involved in getting web fonts set up:

generate @font-face CSS and insert into your existing CSS
generate the full family of web fonts from your TTF or OTF file, then put them someplace the web server can access
add CORS headers to your web server if fonts are served from a separate domain, as Firefox and IE9+ enforce the same origin policy with fonts

These steps are pretty easy to do; the awesome FontSquirrel generator can generate all the missing font files and the @font-face CSS declaration for you. You've still got to sit down with Nginx or Apache docs to figure out how to add the CORS header, but that's not too tough.

If you want to take advantage of font subsetting to hugely improve performance, things become more complex. You'll have font files for each supported locale, and will need to dynamically modify the @font-face CSS declaration to point at the right URL. CORS management is still needed. This is the problem connect-fonts solves.

Font subsetting: overview

By default, font files contain lots of characters: the Latin character set familiar to English speakers; accents and accented characters added to the Latin charset for languages like French and German; additional alphabets like Cyrillic or Greek. Some fonts also contain lots of funny symbols, particularly if they support Unicode (☃ anyone?). Some fonts additionally support East Asian languages. Font files contain all of this so that they can ably serve as many audiences as possible. All this flexibility leads to large file sizes; Microsoft Arial Unicode, which has characters for every language and symbol in Unicode 2.1, weighs in at an unbelievable 22 megabytes.

In contrast, a typical web page only needs a font to do one specific job: display the page's content, usually in just one language, and usually without exotic symbols. By reducing the served font file to just the subset we need, we can shave off a ton of page weight.

Performance gains from font subsetting

Let's compare the size of the localized font files vs the full file size for some common fonts and a few locales. Even if you just serve an English-language site, you can shave off a ton of bytes by serving an English subset.

Smaller fonts mean faster load time and a shorter wait for styled text to appear on screen. This is particularly important if you want to use @font-face on mobile; if your users happen to be on a 2G network, saving 50KB can speed up load time by 2-3 seconds. Another consideration: mobile caches are small, and subsetted fonts have a far better chance of staying in cache.

Open Sans regular, size of full font (default) and several subsets (KB):

Same fonts, gzipped (KB):

Even after gzipping, you can reduce font size 80% by using the English subset of Open Sans (13 KB), instead of the full font (63 KB). Consider that this is the reduction for just one font file--most sites use several. The potential is huge!

Using connect-fonts, Mozilla Persona's font footprint shrank 85%, from 300 KB to just 45 KB. This equates to several seconds of download time on a typical 3G connection.

Going further with optimizations

If you're looking to tweak every last byte and HTTP request, connect-fonts can be configured to return generated CSS as a string instead of a separate file. Going even further, connect-fonts, by default, serves up the smallest possible @font-face declaration, omitting declarations for filetypes not accepted by a given browser.

Example: adding connect-fonts to an app

Suppose you've got a super simple express app that serves up the current time:

// app.js
const
ejs = require('ejs'),
express = require('express'),
fs = require('fs');

var app = express.createServer(),
  tpl = fs.readFileSync(__dirname, '/tpl.ejs', 'utf8');

app.get('/time', function(req, res) {
  var output = ejs.render(tpl, {
    currentTime: new Date()
  });
  res.send(output);
});

app.listen(8765, '127.0.0.1');

with a template like:

// tpl.ejs
<!doctype html>
<p>the time is <%= currentTime %>.

Let's walk through the process of adding connect-fonts to serve the Open Sans font, one of several ready-made font packs.

App changes

Install via npm:

 $ npm install connect-fonts
 $ npm install connect-fonts-opensans

Require the middleware:

 // app.js - updated to use connect-fonts
 const
 ejs = require('ejs'),
 express = require('express'),
 fs = require('fs'),
 // add requires:
 connect_fonts = require('connect-fonts'),
 opensans = require('connect-fonts-opensans');

 var app = express.createServer(),
   tpl = fs.readFileSync(__dirname, '/tpl.ejs', 'utf8');

Initialize the middleware.

  // app.js continued
  // add this app.use call:
  app.use(connect_fonts.setup({
    fonts: [opensans],
    allow_origin: 'http://localhost:8765'
  })

The arguments to connect_fonts.setup() include:

fonts: an array of fonts to enable,
allow_origin: the origin for which we serve fonts; connect-fonts uses this info to set the Access-Control-Allow-Origin header for browsers that need it (Firefox 3.5+, IE 9+)
ua (optional): a parameter listing the user-agents to which we'll serve fonts. By default, connect-fonts uses UA sniffing to only serve browsers font formats they can parse. ua: 'all' overrides this to serve all fonts to all browsers.

Inside your route, pass the user's locale to the template

 // app.js continued
 app.get('/time', function(req, res) {
   var output = ejs.render(tpl, {
     // pass the user's locale to the template
     userLocale: detectLocale(req),
     currentTime: new Date()
   });
   res.send(output);
 });

Detect the user's preferred language. Mozilla Persona uses i18n-abide, and locale is another swell option; both are available via npm. For the sake of keeping this example short, we'll just grab the first two chars from the Accept-Language header.
```
 // oversimplified locale detection
 function detectLocale(req) {
   return req.headers['accept-language'].slice(0,2);
 }

 app.listen(8765, '127.0.0.1');
 // end of app.js
```

Template changes

Now we need to update the template. connect-fonts assumes routes are of the form

    /:locale/:font-list/fonts.css

for example,

    /fr/opensans-regular,opensans-italics/fonts.css

In our case, we'll need to:

add a stylesheet <link> to the template matching the route expected by connect-fonts:

 // tpl.ejs - updated to use connect-fonts
 <!doctype html>
 <link href="/<%= userLocale %>/opensans-regular/fonts.css" rel="stylesheet">

Update the page style to use the new font, and we're done!

 // tpl.ejs continued
 <style>
   body { font-family: "Open Sans", "sans-serif"; }
 </style>
 <p>the time is <%= currentTime %>.

The CSS generated by connect-fonts is based on the user's locale and browser. Here's an example for the 'en' localized subset of Open Sans:

// this is the output with the middleware's ua param set to 'all'.
@font-face {
  font-family: 'Open Sans';
  font-style: normal;
  font-weight: 400;
  src: url('/fonts/en/opensans-regular.eot');
  src: local('Open Sans'),
       local('OpenSans'),
       url('/fonts/en/opensans-regular.eot#') format('embedded-opentype'),
       url('/fonts/en/opensans-regular.woff') format('woff'),
       url('/fonts/en/opensans-regular.ttf') format('truetype'),
       url('/fonts/en/opensans-regular.svg#Open Sans') format('svg');
}

If you don't want to incur the cost of an extra HTTP request, you can use the connect_fonts.generate_css() method to return this CSS as a string, then insert it into your existing CSS files as part of a build/minification process.

That does it! Our little app is serving up stylish timestamps. This example code is available on github and npm if you want to play with it.

We've covered a pre-made font pack, but it's easy to create your own font packs for paid fonts. There are instructions on the connect-fonts readme.

connect-fonts - when to use it & alternatives [todo remove this?]

If you self-host web fonts on a connect-based site, font subsetting can bring huge performance gains. If your site isn't yet internationalized, you can still use just your native subset; connect-fonts will still generate @font-face CSS and handle CORS headers as needed, plus you'll have a smooth upgrade path to internationalize later.

alternatives?

XXX add a target to the 'well-documented' link
XXX how about a table of features showing self-hosted vs third-party service? or is a bulleted list better...

The alternative to hosting your own font files is to use a third-party provider. The pros and cons are well-documented, but things to consider might include:

whether you need fonts to work with JS disabled
- if not, your only third-party option is google font API, and the selection is relatively limited
what happens to your site if the third-party service is slow or goes down (hint: it's not good)
whether the third-party has the fonts you need (maybe not Google) at a price you can afford (maybe not Typekit)

Google and Typekit both provide locale-based subsetting transparently, and their slick, jointly-developed Webfont Loader fires events that make it easier to manage the FOUT.

Wrapping up

connect-fonts is a great tool for self-hosting high performance web fonts. You can get it from github or npm.

Future directions

Today, connect-fonts handles subsetting based on locale. What if it also stripped out font hinting for platforms that don't need it (everything other than Windows)? What if it also optionally gzipped fonts and added far-future caching headers? There's cool work yet to be done. If you'd like to contribute ideas or code, we'd love the help! Grab the source from github and submit issues or pull requests.