Nuxt Fontaine

Font metric override implementation for Nuxt 3

• ✨  Changelog
• ▶️  Online playground

Features

⚠️ @nuxtjs/fontaine is under active development. ⚠️

• 💪 Reduces CLS by using local font fallbacks with crafted font metrics.
• ✨ Generates font metrics and overrides automatically.
• ⚡️ Pure CSS, zero runtime overhead.

On the playground project, enabling/disabling this module makes the following differences rendering /, with no customisation required:

	Before	After
CLS	0.34	0.013
Performance	88	98

What's next

For best performance, you will need to inline all your CSS, not just the font-face override rules (which this module does automatically), or there will still be a layout shift when the stylesheet loads (which is why the number above is not zero).

This PR aims to bring that ability to Nuxt itself.

Installation

With pnpm

pnpm add -D @nuxtjs/fontaine

Or, with npm

npm install -D @nuxtjs/fontaine

Or, with yarn

yarn add -D @nuxtjs/fontaine

Usage

import { defineNuxtConfig } from 'nuxt'

export default defineNuxtConfig({
  modules: ['@nuxtjs/fontaine'],
  // If you are using a Google font or you don't have a @font-face declaration
  // for a font you're using, you can declare them here.
  //
  // In most cases this is not necessary.
  //
  // fontMetrics: {
  //   fonts: ['Inter', { family: 'Some Custom Font', src: '/path/to/custom/font.woff2' }],
  // },
})

That's it!

How it works

Nuxt will scan your @font-face rules and generate fallback rules with the correct metrics. For example:

@font-face {
  font-family: 'Roboto';
  font-display: swap;
  src: url('/fonts/Roboto.woff2') format('woff2'), url('/fonts/Roboto.woff') format('woff');
  font-weight: 700;
}
/* This will be generated. */
@font-face {
  font-family: 'Roboto override';
  src: local('BlinkMacSystemFont'), local('Segoe UI'), local('Roboto'), local('Helvetica Neue'),
    local('Arial'), local('Noto Sans');
  ascent-override: 92.7734375%;
  descent-override: 24.4140625%;
  line-gap-override: 0%;
}

Then, whenever you use font-family: 'Roboto', Nuxt will add the override to the font-family:

:root {
  font-family: 'Roboto';
  /* This becomes */
  font-family: 'Roboto', 'Roboto override';
}

Using outside of Nuxt

The core of this module will work outside of Nuxt, and has been separated into a separate library: fontaine. Check it out!

💻 Development

• Clone this repository
• Enable Corepack using corepack enable (use npm i -g corepack for Node.js < 16.10)
• Install dependencies using pnpm install
• Stub module with pnpm dev:prepare
• Run pnpm dev to start playground in development mode

Credits

This would not have been possible without:

• amazing tooling and generated metrics from capsizecss
• suggestion and algorithm from Katie Hempenius & Kara Erickson on the Google Aurora team - see notes on calculating font metric overrides.

License

Made with ❤️

Published under the MIT License.