gatsby-ssr.js

import React from 'react'
export { wrapRootElement } from './src/apollo/wrapper'

const MagicScriptTag = () => {
  let codeToRunOnClient = `
(function() {
  function getInitialColorMode() {
    const persistedColorPreference =
      window.localStorage.getItem('color-mode');
    const hasPersistedPreference =
      typeof persistedColorPreference === 'string';
    // If the user has explicitly chosen light or dark,
    // let's use it. Otherwise, this value will be null.
    if (hasPersistedPreference) {
      return persistedColorPreference;
    }
    // If they haven't been explicit, let's check the media
    // query
    const mql = window.matchMedia('(prefers-color-scheme: dark)');
    const hasMediaQueryPreference = typeof mql.matches === 'boolean';
    if (hasMediaQueryPreference) {
      return mql.matches ? 'dark' : 'light';
    }
    // If they are using a browser/OS that doesn't support
    // color themes, let's default to 'light'.
    return 'light';
  }

  const colorMode = getInitialColorMode();

  const root = document.documentElement;

  root.style.setProperty('--initial-color-mode', colorMode);
})()`
  // eslint-disable-next-line react/no-danger
  return <script dangerouslySetInnerHTML={{ __html: codeToRunOnClient }} />
}

export const onRenderBody = ({ setPreBodyComponents }) => {
  setPreBodyComponents(<MagicScriptTag />)
}