@fast-ai/gatsby-plugin-staged-fonts

Description

Implementation of Critical FOFT with Data URI

  1. It generates font-faces based on configuration of plugin and inlines the <style> into <head>.
  2. Provides useStagedFonts hook which returns the number of the font loading stage.
  3. Waits till the fonts are loaded before the stage is changed to 1. Compatible with older browsers.

Install

yarn add @fast-ai/gatsby-plugin-staged-fonts -D

or


npm install @fast-ai/gatsby-plugin-staged-fonts -D

How to use

const fontsPath = path.resolve(__dirname, '../files');

const getFontFile = (url) => ({
  url: path.join(fontsPath, url),
});

module.exports = {
	plugins: [{
		resolve: require.resolve('@fast-ai/gatsby-plugin-staged-fonts'),
		options: {
			// Describe your fonts
			fonts: [{
				// Critical fonts are loaded in the critical stage.
				// It should  contains only few glyphs, normally alpha-numeric symbols.
				critical: true,
				files: [
					getFontFile('open-sans-v17-latin-ext_latin-700-critical.woff'),
					getFontFile('open-sans-v17-latin-ext_latin-700-critical.woff2'),
				],
				family: 'Open Sans Critical',
				style: 'normal',
				weight: 400,
			}, {
				files: [
					getFontFile('open-sans-v17-latin-ext_latin-regular.woff'),
					getFontFile('open-sans-v17-latin-ext_latin-regular.woff2'),
				],
				family: 'Open Sans',
				style: 'normal',
				weight: 400,
			}, {
				files: [
					getFontFile('open-sans-v17-latin-ext_latin-700.woff'),
					getFontFile('open-sans-v17-latin-ext_latin-700.woff2'),
				],
				family: 'Open Sans',
				style: 'normal',
				weight: 700,
			}],
		},
	}]
};

Options

  • alwaysLoadCriticalsFirst (boolean) - if true, the session storage will not be used and the stage 0 will always happen, meaning that critical fonts will be always used. This will eliminate FOUT but not the FOFT.
  • fonts (arrayOf(FontDescription)) - Description of fonts used by the gatsby application

FontDescription

  • critical (boolean) - if true, the font will be loaded in stage 0. Font files with this flag will be base64-encoded and inlined as a data URI in generated @font-faces.
  • family (string) - Name of the font-family
  • style (string) - Style of the font
  • weight (string|number) - Weight of the font
  • files (arrayOf(FontFile)) - Font files

FontFile

  • url (string) - “URL” of self-hosted font, meaning it should lead to file system. Font will be copied to the public folder.

Hooks

useStagedFonts

Returns the actual stage of font loading.

useStagedFonts(options): props

options (object)

stage (number)
  • 0 - only critical fonts are loaded. Use only critical font families
  • 1 - all fonts loaded it is safe to switch to non-critical font-families.
isCriticalStage (boolean)

Alias for stage === 0.

Example - with css class

import { useStagedFonts } from '@fast-ai/gatsby-plugin-staged-fonts';

const AppWithFonts = (props) => {
	const { isCriticalStage } = useStagedFonts();

	useEffect(
		() => {
			if (!isCriticalStage) {
				document.documentElement.className += " fonts-loaded";
			}
		},
		[isCriticalStage]
	);

	return <App {...props} />
};

Example - with Rebass

import { useStagedFonts } from '@fast-ai/gatsby-plugin-staged-fonts';

const Theme = ({ theme, ...rest }) => {
	const { isCriticalStage } = useStagedFonts();

	const themeWithResolvedFonts = useMemo(
		() => ({
			...theme,
			fonts: isCriticalStage
				// use critical fonts which are base64 encoded
				? {
						body: 'Roboto Critical',
						heading: 'Open Sans Critical',
					}
				: {
						body: 'Roboto',
						heading: 'Open Sans',
						mono: 'Roboto Mono',
					},
		}),
		[theme, isCriticalStage]
	);

	return <ThemeProvider theme={themeWithResolvedFonts} {...rest} />;
};

More examples

See the @fast-ai themes:

FAQ

What is “critical” font?

It is a version of the “full” font, which contains only small amount of glyphs, normally only alpha-numeric characters. Meaning the font size is much smaller than a full blown font file.

TODO

  • local name of font
@font-face {
	font-family: 'Roboto';
	font-style: normal;
	font-weight: 100;
	src: local('Roboto Thin'), local('Roboto-Thin'),
			 url('./files/roboto-v20-latin-ext_latin-100.eot?#iefix') format('embedded-opentype');
}

License

All packages are distributed under the MIT license. See the license here.

© 2021 Lundegaard a.s.