Avoid invisible text during font loading
- Display text immediately
- Option #1: Use font-display
- Option #2: Wait to use custom fonts until they are loaded
- Verify
Fonts are often large files that take awhile to load. To deal with this, some browsers hide text until the font loads (the "flash of invisible text"). If you're optimizing for performance, you'll want to avoid the "flash of invisible text" and show content to users immediately using a system font (the "flash of unstyled text").
Display text immediately
This guide outlines two ways to achieve this: the first approach is very simple but does not have universal browser support; the second approach is more work but has full browser support. The best choice for you is the one that you'll actually implement and maintain.
Option #1: Use font-display
| Before | After |
|---|---|
@font-face {
font-family: Helvetica;
}
|
@font-face {
font-family: Helvetica;
font-display: swap;
}
|
font-display
is an API for specifying font display strategy. swap tells the browser that
text using this font should be displayed immediately using a system font. Once
the custom font is ready, the system font is swapped out.
{% BrowserCompat 'css.at-rules.font-face.font-display' %}
If a browser does not support font-display, the browser continues to follow
its default behavior for loading fonts.
These are the default font-loading behaviors for common browsers:
| Browser | Default behavior if font is not ready… |
|---|---|
| Edge | Uses a system font until font is ready. Swaps out font. |
| Chrome | Will hide text for up to 3 seconds. If text is still not ready, uses a system font until font is ready. Swaps out font. |
| Firefox | Will hide text for up to 3 seconds. If text is still not ready, uses a system font until font is ready. Swaps out font. |
| Safari | Hides text until font is ready. |
Option #2: Wait to use custom fonts until they are loaded
With a bit more work, the same behavior can be implemented to work across all browsers.
There are three parts to this approach:
- Don't use a custom font on initial page load. This ensures that the browser displays text immediately using a system font.
- Detect when your custom font is loaded. This can be accomplished with a couple lines of JavaScript code, thanks to the FontFaceObserver library.
- Update page styling to use the custom font.
Here are the changes you can expect to make to implement this:
- Refactor your CSS to not use a custom font on initial page load.
- Add a script to your page. This script detects when the custom font is loaded and then will update the page styling.
{% Aside 'codelab' %} Use Font Face Observer to display text immediately. {% endAside %}
Verify
Run Lighthouse to verify the site is using font-display: swap to display
text:
{% Instruction 'audit-performance', 'ol' %}
Confirm that the Ensure text remains visible during webfont load audit is passing.