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 font = new FontFacePreloader('My Family', {
  weight: 400
});

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

The FontFacePreloader 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 load 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 load method.

var font = new FontFacePreloader('My Family');

font.load('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 load method.

var font = new FontFacePreloader('My Family');

font.load(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 FontFacePreloader instance for each.

var fontA = new FontFacePreloader('Family A');
var fontB = new FontFacePreloader('Family B');

fontA.load().then(function () {
  console.log('Family A is available');
});

fontB.load().then(function () {
  console.log('Family B is available');
});

You may also load both at the same time, rather than loading each individually.

var fontA = new FontFacePreloader('Family A');
var fontB = new FontFacePreloader('Family B');

Promise.all([fontA.load(), fontB.load()]).then(function () {
  console.log('Family A & B have loaded');
});

The following example emulates FOUT with Font Face Observer for "My Family".

var font = new FontFacePreloader('My Family');

font.load().then(function () {
  document.documentElement.className += " fonts-loaded";
});

.fonts-loaded {
  body {
    font-family: My Family, sans-serif;
  }
}

Installation

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

$ npm install fontface-preloader

You can then require fontface-preloader as a CommonJS (Browserify) module:

var FontFacePreloader = require('fontface-preloader');

var font = new FontFacePreloader('My Family');

font.load().then(function () {
  console.log('My Family has loaded');
});

If you're not using npm, grab fontface-preloader.js or fontface-preloader.standalone.js (see below) and include it in your project. It'll export a global FontFacePreloader 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 fontface-preloader.standalone.js in your project. If you do not have an existing Promise polyfill you should use fontface-preloader.js which includes a small Promise polyfill. Using the Promise polyfill adds roughly 1.4KB (500 bytes gzipped) to the file size.

Browser support

FontFacePreloader has been tested and works on the following browsers:

• Chrome (desktop & Android)
• Firefox
• Opera
• Safari (desktop & iOS)
• IE8+
• Android WebKit

License

Font Face Observer is licensed under the BSD License. Copyright 2014-2016 Bram Stein. All rights reserved.