Font Face Observer

Font Face Observer is a small @font-face loader and monitor (3.5KB minified and 1.3KB 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.

How to use

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 arguments: the font family name (required) and an object describing the variation (optional). The object can contain weight, style, and stretch 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('中国').then(function () {
  console.log('Font is available');
}, function () {
  console.log('Font is not available');
});

The default timeout for giving up on font loading is 3 seconds. You can increase or decrease this by passing a number of milliseconds as the second parameter to the check method.

var observer = new FontFaceObserver('My Family');

observer.check(null, 5000).then(function () {
  console.log('Font is available');
}, function () {
  console.log('Font is not available after waiting 5 seconds');
});

Multiple fonts can be loaded by creating a FontFaceObserver instance for each.

var observer = new FontFaceObserver('Family A');
var observer2 = new FontFaceObserver('Family B');

observer.check().then(function () {
  console.log('Family A is available');
});

observer2.check().then(function () {
  console.log('Family B is available');
});

You may also check both are loaded, rather than checking each individually.

var observer = new FontFaceObserver('Family A');
var observer2 = new FontFaceObserver('Family B');

Promise.all([observer.check(), observer2.check()]).then(function () {
  console.log('Family A & B have loaded');
});

Installation

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

$ npm install fontfaceobserver

You can then require fontfaceobserver as a CommonJS (Browserify) module:

var FontFaceObserver = require('fontfaceobserver');

var observer = new FontFaceObserver('My Family');

observer.check().then(function () {
  console.log('My Family has loaded');
});

If you're not using npm, grab fontfaceobserver.js or fontfaceobserver.standalone.js (see below) and include it in your project. It'll export a global FontFaceObserver that you can use to create new instances.

Font Face Observer uses Promises in its API, so for browsers that do not support promises you'll need to include a polyfill. If you use your own Promise polyfill you just need to include fontfaceobserver.standalone.js in your project. If you do not have an existing Promise polyfill you should use fontfaceobserver.js which includes a small Promise polyfill. Using the Promise polyfill adds roughly 1.4KB (500 bytes gzipped) to the file size.

Browser support

FontFaceObserver has been tested and works on the following browsers:

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

License

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