Optimizing Web Fonts with Webfont Loader

Contents

Optimizing Web Fonts with Webfont Loader

Web fonts can dramatically enhance the visual appeal of a website, but they also introduce performance challenges such as FOIT (Flash of Invisible Text) and FOUT (Flash of Unstyled Text). Webfont Loader—an open-source JavaScript library co-maintained by Google and Adobe—enables fine-grained control over web font loading behavior, ensuring an optimal balance between aesthetics and performance.

Why Optimize Web Fonts

Reduce Render-Blocking: Fonts loaded synchronously can delay page rendering.
Prevent FOIT/FOUT: Control fallback strategies and swap behavior.
Improve Perceived Performance: Show system fonts immediately, then swap in web fonts.
Leverage Caching Subsetting: Only load necessary characters and formats.

Introducing Webfont Loader

Webfont Loader provides an API for asynchronously loading fonts from multiple providers (Google, Typekit, Fontdeck, custom). It emits events during the font loading lifecycle, giving you hooks to apply classes or inline styles, achieving precise control over font rendering:

fontloading: A font has begun loading.
fontactive: A font has successfully loaded and applied.
fontinactive: A font failed to load.
active: All specified fonts have loaded.
inactive: Some or all fonts failed to load.

Official repository: https://github.com/typekit/webfontloader

1. Installation Setup

CDN:

ltscript src=https://ajax.googleapis.com/ajax/libs/webfont/1.6.26/webfont.jsgtlt/scriptgt

npm / yarn:
```
npm install webfontloader
      
```

2. Basic Configuration

Below is an example loading Google Fonts and a custom provider in the same call:

WebFont.load({
  google: {
    families: [Roboto:400,700, Open Sans]
  },
  custom: {
    families: [MyIconFont],
    urls: [https://example.com/fonts/myiconfont.css]
  },
  fontactive: function(familyName, fvd) {
    console.log(familyName       fvd    loaded)
  },
  inactive: function() {
    console.warn(One or more fonts failed to load)
  }
})

3. Handling FOIT FOUT

Combine Webfont Loader with CSS @font-face strategies:

Use font-display: swap to display fallback fonts until the web font loads.
In JavaScript callbacks, apply classes:

WebFont.load({
  google: { families: [Lato] },
  classes: false,
  loading: function() {
    document.documentElement.classList.add(wf-loading)
  },
  active: function() {
    document.documentElement.classList.remove(wf-loading)
    document.documentElement.classList.add(wf-active)
  },
  inactive: function() {
    document.documentElement.classList.remove(wf-loading)
    document.documentElement.classList.add(wf-inactive)
  }
})

Then in CSS:

.wf-loading body {
  font-family: Arial, sans-serif
}
.wf-active body {
  font-family: Lato, Arial, sans-serif
}

4. Preloading Subsetting

To reduce load times further:

Preload key fonts:

ltlink rel=preload href=/fonts/Roboto.woff2 as=font type=font/woff2 crossorigingt

Subset font files to include only needed glyphs (e.g., Latin, Cyrillic).

5. Comparing Font Formats

Format	Compression	Browser Support
WOFF2	High	Latest browsers
WOFF	Medium	Broad support
TTF/OTF	Low	Fallback only

Best Practices Checklist

Use font-display in @font-face rules.
Preload critical fonts with ltlink rel=preloadgt.
Choose appropriate font formats (WOFF2 WOFF).
Implement fallback stacks for system fonts.
Leverage Webfont Loader events for dynamic class toggling.
Subset font files to reduce file size.

Optimizing Web Fonts with Webfont Loader