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                <h1>Smarter web font loading and caching</h1>
<p>Based on The Guardian website. Web fonts are loaded, cached and applied using the following logic:</p>
  <li>Pre-render: if the fonts are in localstorage apply immediately, else do nothing!</li>
  <li>Post-render: if the fonts are not yet in localstorage (but localstorage is available) and the browser supports WOFF (not yet implemented, how do I detect this?) download base64 encoded fonts in JSON format, store and apply them.</li>
<p>The advantage of this approach is that you can have a custom web font without performance hit or invisible text while the browser is downloading the font (this behavior differs per browser).</p>
<p>Wrote an article about this, read it on <a href="" target="_blank">my blog</a>!


                html {
  margin: 0.75em;
  color: #444;
  font: 300 100%/1.5 Ubuntu, sans-serif;

h1 {
  font: 400 2.5em/1 Alegreya, serif;

a {
  color: #444;


 * Should be in the head to prevent FOUT on subsequent page views.
 * Make sure to edit md5 and path to your fonts json!
(function(window, document) {
  'use strict';

  var isModernBrowser = (
        'querySelector' in document &&
        'localStorage' in window &&
        'addEventListener' in window
      md5 = 'e90ba95faca6e63b5516ed839f4514ec',
      key = 'fonts',

  if (!isModernBrowser) {
    // Sorry, browser is too old!

  function insertFont(value) {
    var style = document.createElement('style');
    style.innerHTML = value;

  try {
    cache = window.localStorage.getItem(key);
    if (cache) {
      cache = JSON.parse(cache);
      if (cache.md5 == md5) {
      } else {
        // Busting cache when md5 doesn't match
        cache = null;
  } catch(e) {
    // Most likely LocalStorage disabled, so hopeless...
  if (!cache) {
    window.addEventListener('load', function() {
      var request = new XMLHttpRequest(),
          response;'GET', '', true);
      request.onload = function() {
        if (this.status == 200) {
          try {
            response = JSON.parse(this.response);
            window.localStorage.setItem(key, this.response);
          } catch(e) {
            // LocalStorage is probably full
})(window, document);

 * Inspired by: