Next.js - How to optimize fonts

Hey there! There is now next/font that does this way better. Use that instead

When using 3rd party fonts we have to make sure they are optimized, in the times before Next.js 10.2 you had to manually optimize them for example:

<link rel="preconnect" href="https://fonts.googleapis.com" />
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
<link
    href="https://fonts.googleapis.com/css2?family=Merriweather+Sans&display=swap"
    rel="stylesheet"
/>
<link
    href="https://fonts.googleapis.com/css2?family=Squada+One:wght@400&display=swap"
    rel="stylesheet"
/>
html

After 10.2 Next.js can now optimize Google fonts and Typekit with a variety of font optimization, inside your _document.js you can now provide the font:

import Document, { Html, Head, Main, NextScript } from 'next/document'

class MyDocument extends Document {
  render() {
    return (
      <Html>
        <Head>
          <link
            href="https://fonts.googleapis.com/css2?family=Inter&display=optional"
            rel="stylesheet"
          />
        </Head>
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    )
  }
}

export default MyDocument
jsx

You can even provide the preferred display options as a query parameter :

- block : The text blocks (is invisible) for a short period

- swap: There is no block period (so no invisible text), and the text is shown immediately in the fallback font until the custom font loads

- fallback: This is somewhere in between block and swap. The text is invisible for a short period of time (100ms). Then if the custom font hasn't been downloaded, the text is shown in a fallback font (for about 3s), then swapped after the custom font loads.

- optional: This behaves just like fallback, only the browser can decide to not use the custom font at all, based on the user's connection speed (if you're on a slow 3G or less, it will take forever to download the custom font and then swapping to it will be too late and extremely annoying)

- auto: This basically ends up being the same as fallback.