Font Face Observer is a small @font-face loader and monitor (2.7KB minified and 1.1KB gzipped) compatible with any web-font service. It will monitor when a web font is applied to the page and notify you. It does not limit you in any way in where, when, or how you load your web fonts. Unlike the Web Font Loader Font Face Observer uses scroll events to detect font loads efficiently and with minimum overhead.

Include your @font-face rules as usual. Fonts can be supplied by either a font service such as Google Fonts, Typekit, and Webtype or be self-hosted. It doesn't matter where, when, or how you load your fonts. You can set up monitoring for a single font family at a time:

var observer = new FontFaceObserver('My Family', {
  weight: 400
});

observer.check().then(function () {
  console.log('Font is available');
}, function () {
  console.log('Font is not available');
});

The FontFaceObserver constructor takes two (required) arguments: the font family name and an object describing the variation. The object can contain weight, style, stretch, variant, and featureSettings properties. If a property is not present it will default to normal. To start observing font loads, call the check method. It'll immediately return a new Promise that resolves when the font is available and rejected when the font is not available.

If your font doesn't contain latin characters you can pass a custom test string to the check method.

var observer = new FontFaceObserver('My Family', {});

observer.check('**').then(function () {
  console.log('Font is available');
}, function () {
  console.log('Font is not available');
});

If you're using npm you can install Font Face Observer as a dependency:

> npm install fontfaceobserver

You can then either include fontfaceobserver.js or fontfaceobserver.standalone.js. The former is Font Face Observer without dependencies. The latter includes a small promise polyfill.

If you're not using npm, grab either fontfaceobserver.js or fontfaceobserver.standalone.js and include it in your project.

FontFaceObserver has been tested and works on the following browsers:

• Chrome (desktop & Android)
• Firefox
• Opera
• Safari (desktop & iOS)
• IE9+
• Android WebKit

FontFaceObserver is licensed under the BSD License. Copyright 2014-2015 Bram Stein. All rights reserved.