By Shad Super in Questions —

What Role Do Web Fonts Play in Affecting First Input Delay (FID), and How Can I Optimize Their Loading to Reduce Impact?

Summary

Web fonts significantly influence First Input Delay (FID), a crucial metric for user experience on the web. Optimizing web font loading can enhance FID by reducing the time users spend waiting for the first interaction to be processed. This guide details ways to optimize web fonts effectively to minimize their impact on FID.

Understanding First Input Delay (FID)

What is FID?

First Input Delay (FID) measures the time from when a user first interacts with a page (e.g., clicking a link, tapping a button) to the time when the browser is actually able to respond to that interaction. A low FID is critical for good user experience.

The Impact of Web Fonts on FID

Web fonts can block the rendering of text until the fonts are fully downloaded and rendered. This leads to increased FID as the browser might be busy fetching and rendering these fonts instead of responding to user interactions. Optimizing the loading of web fonts can help in mitigating this delay.

Optimizing Web Fonts to Reduce FID

Preloading Fonts

Preloading web fonts can help ensure they are available earlier in the rendering process.

<link rel="preload" href="path/to/font.woff2" as="font" type="font/woff2" crossorigin></pre>

Utilizing the preload link will ensure that font files are one of the first resources to be fetched by the browser, reducing the time they take to load and render.

[Optimize Web Fonts, 2023]

Using Font Display Options

The font-display property in CSS allows control over how a font renders depending on whether it's loaded or not. Setting it to swap ensures that a fallback font is displayed immediately until the custom font is loaded.

@font-face {
font-family: 'MyFont';
src: url('path/to/font.woff2') format('woff2');
font-display: swap;
}

This helps ensure that text remains visible while the font loads, improving FID by not blocking interaction.

[Controlling Font Performance with Font Display, 2023]

Subsetting Fonts

Loading only the characters or character sets needed for your webpage is known as subsetting. This reduces the font file size and decreases the time needed to load fonts.

Tools such as Glyphhanger can assist in creating subsets of fonts.

[Web Font Best Practices, 2022]

Preconnect to Font Origins

To speed up the connection process to font hosting servers, using preconnect can establish early connections to external font origins.

<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin></pre>

This step ensures that the browser can start fetching fonts more quickly by eliminating round-trip time delays in DNS resolution and TLS handshakes.

[Preconnect for Web Performance, 2023]

Asynchronous Font Loading

Loading fonts asynchronously ensures that the rest of the webpage is not blocked while web fonts are being fetched.

Using JavaScript libraries like Web Font Loader can manage font loading more effectively and provide fallback options when fonts are not available immediately.

[Google Fonts Optimization, 2023]

Conclusion

Optimizing web font delivery through preloading, font display settings, subsetting, preconnect, and asynchronous loading can significantly improve First Input Delay (FID). Implementing these best practices ensures that web fonts do not become a bottleneck in user interaction and page load times, creating a smoother and more responsive user experience.


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