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Control Font Fallbacks with the CSS Font Loading API in JavaScript

Last updated: December 12, 2024

When designing websites, fonts play a crucial role in conveying visual identity and enhancing user experience. However, ensuring that the right fonts load consistently across all browsers and devices can be challenging. This is where the CSS Font Loading API comes in handy, offering an advanced way to control font loading and fallbacks using JavaScript.

Understanding the Basics of CSS Font Loading API

The CSS Font Loading API provides a programmatic way to load and control fonts. It allows developers to check the status of fonts, load fonts asynchronously, and get notified when fonts have been loaded effectively. The key interface provided by this API is the FontFace and the FontFaceSet.

FontFace Interface

The FontFace interface represents a single usable font and provides access to various attributes such as family, style, and weight. You can create a new instance of a FontFace like this:

const fontFace = new FontFace('MyFont', 'url(/path/to/font.woff2)');

This creates a new font face with the given font-family and the URL where the font is located.

FontFaceSet Interface

The FontFaceSet represents the set of fonts used in a document. It helps in controlling, observing, and listening to events such as when fonts are loading or are loaded. Typically, it is accessed via document.fonts.

document.fonts.add(fontFace);
fontFace.load().then(() => {
    console.log('Font loaded successfully!');
});

Controlling Font Fallbacks with JavaScript

Font fallbacks are essential when the designated primary font fails to load. The CSS Font Loading API allows developers to address this problem more dynamically compared to CSS alone.

Adding Async Font Loading and Management

Here is how you can load fonts asynchronously and detect fallback scenarios:

const fontFace = new FontFace('Fira Sans', 'url(/fonts/fira-sans.woff2)', {
    style: 'normal',
    weight: '400'
});

document.fonts.add(fontFace);

document.fonts.ready.then(() => {
    console.log('All fonts in the document have been loaded.');
}).catch((error) => {
    console.error('Some fonts failed to load:', error);
});

You can use the ready property, which returns a promise that resolves when all the document fonts are loaded.

Handling Fallbacks Gracefully

In case a font fails to load, you might want to switch to a fallback. Here is an example where we use a default font if the primary one fails:

fontFace.load().then(loadedFace => {
    document.fonts.add(loadedFace);
    document.body.style.fontFamily = 'Fira Sans, Arial, sans-serif';
}).catch(error => {
    console.error('Failed to load Fira Sans, switching to fallback...', error);
    document.body.style.fontFamily = 'Arial, sans-serif';
});

This script attempts to load 'Fira Sans', and if unsuccessful, defaults to 'Arial'.

Browser Support and Considerations

As of the latest data, the CSS Font Loading API is supported in most modern browsers, but it's always good to check compatibility on resources like caniuse.com. This API offers a robust way of dealing with font loading, yet still requires consideration of users with older browsers.

Integrating the CSS Font Loading API provides many flexibilities in managing web fonts, improving performance by loading only necessary fonts, and enriching user experience with reliable fallbacks.

Conclusion

Font management has considerably improved with the CSS Font Loading API, empowering developers with better control over dynamic aspects of typography on the web. Through methods like asynchronous loading and fallback handling, your websites can become more resilient, performant, and visually appealing.

Next Article: Register Custom CSS Properties with the Properties and Values API in JavaScript

Previous Article: Preload Fonts Using the CSS Font Loading API in JavaScript

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