Reddit System Theme Switch UserScript

reddit-system-theme-switch-userscript.js

// ==UserScript==
// @name         Reddit System Theme Switch
// @namespace    http://tampermonkey.net/
// @version      1.0
// @description  Auto switch Reddit light/dark mode based on system theme. Based on new Reddit UI.
// @author       Denis Semenenko <[email protected]>
// @match        https://*.reddit.com/*
// @grant        none
// ==/UserScript==

(function () {
  'use strict';

  function syncTheme() {
    const modeSwitch = document.querySelector('[name=darkmode-switch-name]');
    if (!modeSwitch) {
      return console.warn(`Dark mode switch not found on reddit.com, skipping auto dark mode.`);
    }
    const isLightToggled = modeSwitch.getAttribute('checked') === null;
    const lightMode = window.matchMedia('(prefers-color-scheme: light)').matches;
    if (isLightToggled !== lightMode) {
      modeSwitch.click();
    }
  }

  window.addEventListener('load', () => {
    syncTheme();
    window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', syncTheme);
  });
})();