theme.js

/*!
 * Color mode toggler for Bootstrap's docs (https://getbootstrap.com/)
 * Copyright 2011-2023 The Bootstrap Authors
 * Licensed under the Creative Commons Attribution 3.0 Unported License.
 *
 * Based on the below, with some changes for the datatracker:
 * https://github.com/twbs/bootstrap/blob/main/site/static/docs/5.3/assets/js/color-modes.js
 */

(() => {
  'use strict'

  const getStoredTheme = () => localStorage.getItem('theme') || 'auto'
  const setStoredTheme = theme => localStorage.setItem('theme', theme)

  const getPreferredTheme = () => {
    const storedTheme = getStoredTheme()
    if (storedTheme) {
      return storedTheme
    }

    return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
  }

  const setTheme = theme => {
    if (theme === 'auto') {
        if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
          document.documentElement.setAttribute('data-bs-theme', 'dark')
        } else if (window.matchMedia('(prefers-color-scheme: light)').matches) {
          document.documentElement.setAttribute('data-bs-theme', 'light')
        }
    } else {
      document.documentElement.setAttribute('data-bs-theme', theme)
    }
  }

  setTheme(getPreferredTheme())

  const showActiveTheme = (theme, focus = false) => {
    const themeSwitcher = document.querySelector('#bd-theme')

    if (!themeSwitcher) {
      return
    }

    // Commented-out lines are from the original bs5 js, which uses a more complicated pref dropdown.
    // Kept them here for easier future diffing.
    const themeSwitcherText = document.querySelector('#bd-theme-text')
    const activeThemeIcon = document.querySelector('.theme-icon-active')
    const btnToActive = document.querySelector(`[data-bs-theme-value="${theme}"]`)
    const iconPattern = new RegExp(/\bbi-[\w-]+\b/);
    const iconOfActiveBtn = btnToActive.querySelector('i').className.match(iconPattern)[0]

    document.querySelectorAll('[data-bs-theme-value]').forEach(element => {
      element.classList.remove('active')
      element.setAttribute('aria-pressed', 'false')
    })

    btnToActive.classList.add('active')
    btnToActive.setAttribute('aria-pressed', 'true')
    if (activeThemeIcon) {
        activeThemeIcon.className = activeThemeIcon.className.replace(iconPattern, iconOfActiveBtn)
    }
    if (themeSwitcherText) {
        const themeSwitcherLabel = `${themeSwitcherText.textContent} (${btnToActive.dataset.bsThemeValue})`
        themeSwitcher.setAttribute('aria-label', themeSwitcherLabel)
    }
    if (focus) {
      themeSwitcher.focus()
    }
  }

  window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
    const storedTheme = getStoredTheme()
    if (storedTheme !== 'light' && storedTheme !== 'dark') {
      setTheme(getPreferredTheme())
    }
  })

  window.addEventListener('DOMContentLoaded', () => {
    showActiveTheme(getPreferredTheme())

    document.querySelectorAll('[data-bs-theme-value]')
      .forEach(toggle => {
        toggle.addEventListener('click', () => {
          const theme = toggle.getAttribute('data-bs-theme-value')
          setStoredTheme(theme)
          setTheme(theme)
          showActiveTheme(theme, true)
        })
      })
  })
})()