The Best Font Loading Strategies and How to Execute Them

Mastering Web Font Loading Strategies: A Practical Guide

Zach Leatherman's comprehensive guide to font loading strategies has been a valuable resource for web developers. However, the sheer number of options can be overwhelming. This article simplifies the best approaches, focusing on practicality and execution.

Key Strategies:

Leatherman champions two primary strategies:

1. FOUT with Class: A versatile approach suitable for most scenarios, regardless of whether fonts are self-hosted or utilize a font-hosting service.
2. Critical FOFT: The most performant option, but limited to self-hosted fonts.

Before delving into these, let's clarify the terminology:

• FOIT (Flash of Invisible Text): Text is hidden until the web font loads.
• FOUT (Flash of Unstyled Text): A system font is displayed initially, then replaced by the web font.
• FOFT (Flash of Faux Text): A more complex method involving loading the Roman font first, then other styles.

Font Hosting Options:

1. Cloud Providers (e.g., Google Fonts, Adobe Fonts): Generally easier to implement, but often less performant due to blocking behavior. Google Fonts' display=swap parameter offers a slight improvement by enabling FOUT.

   <link href="https://fonts.googleapis.com/css2?family=Lato:ital,wght@0,400;0,700;1,400;1,700&display=swap" rel="stylesheet">

2. Self-Hosting: Requires font licenses and involves using @font-face and potentially font-display: swap. This allows for greater control and optimization.

Self-Hosted Fonts and Implementation:

@font-face allows font declaration in CSS:

@font-face {
  font-family: Lato;
  src: url('path-to-lato.woff2') format('woff2'),
       url('path-to-lato.woff') format('woff');
  /* ... other weights and styles ... */
}

html {
  font-family: Lato, sans-serif;
}

font-display: swap triggers FOUT for self-hosted fonts.

FOUT with Class (for both Cloud and Self-Hosted Fonts):

This strategy uses JavaScript to load fonts asynchronously, grouping repaints and adapting to user preferences. It also allows skipping font loading if the user already has the font installed.

1. Load fonts normally (via <link> for cloud-hosted or @font-face for self-hosted).

2. Use the CSS Font Loading API (or FontFaceObserver for broader compatibility) in a <script></script> tag:

   if ('fonts' in document) {
     Promise.all([
       document.fonts.load('1em Lato'),
       // ... other weights and styles ...
     ]).then(_ => {
       document.documentElement.classList.add('fonts-loaded');
     });
   }

3. Use CSS to style the text:

   body {
     font-family: sans-serif; /* System font */
   }
   
   .fonts-loaded body {
     font-family: Lato, sans-serif; /* Web font */
   }

4. Optimize for repeat visits using sessionStorage:

   if (sessionStorage.fontsLoaded) {
     document.documentElement.classList.add('fonts-loaded');
   } else {
     // ... font loading code ...
   }

FOFT (Flash of Faux Text):

This advanced technique loads the Roman font first, then other styles. "Critical FOFT" optimizes this by loading only essential characters initially. While offering performance gains, it's more complex to implement.

Choosing the Right Strategy:

• Cloud-Hosted, Simple: Use font-display: swap if provided by the host; otherwise, use FOUT with Class.
• Self-Hosted, Simple: @font-face font-display: swap is the easiest approach, especially for a small number of font files.
• Self-Hosted, Advanced: Consider Standard FOFT or Critical FOFT for performance optimization, especially with many font files.

This streamlined guide provides a clear path to choosing and implementing the optimal font loading strategy for your project. Remember to prioritize a JavaScript-free approach when feasible, particularly with limited font files.

The above is the detailed content of The Best Font Loading Strategies and How to Execute Them. For more information, please follow other related articles on the PHP Chinese website!