There is two main files, fonts.js and fallback.js. First is a core file, it contains main methods and code to load fonts with Fonts Loading API. Second is a fallback which is used when Fonts Loading API is not available. You can inline both files in page's html or just inline fonts.js and load fallback.js when needed.

• fonts.min.js is 1.36 KB
• fallback.min.js is 5.3 KB

Basic example:

<script>
  // Inline contents of fonts.js
  <%= fonts_js_file %>

  var fontSrc = 'local('Roboto'), local('Roboto-Regular'), url(https://fonts.gstatic.com/s/roboto/v15/oMMgfZMQthOryQo9n22dcuvvDin1pK8aKteLpeZ5c0A.woff2) format('woff2'), url(https://fonts.gstatic.com/s/roboto/v15/CrYjSnGjrRCn0pd9VQsnFOvvDin1pK8aKteLpeZ5c0A.woff) format('woff')';

  // Set url of a fallback file to be loaded when Fonts Loading API is not available
  Fonts.FALLBACK_FILE = 'fallback.js';
  Fonts.load([
    new Fonts.Font(fontSrc, 'Roboto', 700, 'normal'),
  ], function onLoad() {
    // Add class which uses loaded font
    document.body.className += ' fonts';
  }, function onError() {
    // ...
  });
</script>

Fonts.load(fonts: Array<Fonts.Font>, onLoad?: Function, onError?: Function);

Loads passed Fonts.

new Fonts.Font(source: string, family: string, weight?: number, style?: string, text?: string);

Creates Font object which can be used by Fonts Loading API or fallback.js.

Fonts.setSample(fontType: string, text: string);

Sets text samples to test fonts existence.

Example 1: Fonts.setSample('16px Roboto', 'тест') to test cyrilic text

Example 2:

var font = new Fonts.Font('...', 'Roboto');

Fonts.setSample(Fonts.getFontType(font), 'тест');

Fonts.load([font], ...);

Does same as Example 1, but uses getFontType(font: Fonts.Font) method to stringify Font to font (CSS's font property value) and then re-uses same Font to load it.

Fonts.USE_FONTS_API: boolean;

Set to false before calling load() to prevent usage of Fonts Loading API.

Example: Fonts.USE_FONTS_API = false;

Description about fallback.js implementation will be added later. Still may have bugs, of course.

MIT