Trigger and monitor the loading of custom fonts on AMP pages.
<script async custom-element="amp-font" src="https://cdn.ampproject.org/v0/amp-font-0.1.js"></script>
amp-font extension should be used for controlling timeouts on font loading.
amp-font extension allows adding and removing CSS classes from
document.body based on whether a font was loaded or is in error-state.
<amp-font layout="nodisplay" font-family="My Font" timeout="3000" on-error-remove-class="my-font-loading" on-error-add-class="my-font-missing" ></amp-font> <amp-font layout="nodisplay" font-family="My Other Font" timeout="1000" on-load-add-class="my-other-font-loaded" on-load-remove-class="my-other-font-loading" ></amp-font>
The extension observes loading of a font and when it loads executes the optional attributes
on-load-remove-class and when there is any error or timeout runs
These classes are toggled on the
documentElement for standalone documents, and on
body for documents
documentElement i.e. inside a
Using these classes authors can guard whether a font is displayed and get the following results:
- get a short (e.g. 3000ms) timeout in Safari similar to other browsers
- implement FOIT where the page renders with no text before the font comes in
- make the timeout very short and only use a font if it was already cached.
amp-font extension accepts the
|font-family||The font-family of the custom font being loaded.|
|timeout||Time in milliseconds after which the we don't wait for the custom font to be available. This attribute is optional and it's default value is 3000. If the timeout is set to 0 then the amp-font loads the font if it is already in the cache, otherwise the font would not be loaded. If the timeout is has an invalid value then the timeout defaults to 3000.|
|on-load-add-class||CSS class that would be added to the document root after making sure that the custom font is available for display. This attribute is optional.|
|on-load-remove-class||CSS class that would be removed from the document root after making sure that the custom font is available for display. This attribute is optional.|
|on-error-add-class||CSS class that would be added to the document root if the timeout interval runs out before the font becomes available for use. This attribute is optional.|
|on-error-remove-class||CSS class that would be removed from the document root if the timeout interval runs out before the font becomes available for use. This attribute is optional.|
|font-weight, font-style, font-variant||The attributes above should all behave like they do on standard elements.|
|layout||Must be |
See amp-font rules in the AMP validator specification.