0Pricing
Tailwind CSS Academy · Aula

Criação de um alternador do modo escuro

Implemente um alternador em JavaScript que adicione e remova a classe dark do elemento html e persista a preferência em localStorage.

Criação de um alternador do modo escuro é uma aula grátis de Tailwind CSS Academy no CoddyKit. Esta é a aula 3 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Tailwind CSS Academy, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Tailwind CSS Academy inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

What the Toggle Needs to Do

A dark mode toggle needs to accomplish three things: read the user's saved preference (or OS preference as a fallback), apply the correct class to the <html> element on page load, and update the class and save the preference when the user clicks the toggle button. Getting the initial load right is critical — applying the class before the page renders prevents a flash of incorrect theme.

Preventing Flash of Wrong Theme

The most common dark mode bug is a flash of light theme when a user in dark mode refreshes the page. This happens because JavaScript runs after the HTML has already been parsed and rendered. The fix is to run a tiny inline <script> in the <head> — before any CSS or body content — that reads localStorage and immediately adds the dark class if needed.

<!-- Place this FIRST inside <head> -->
<script>
  if (localStorage.theme === 'dark' ||
      (!('theme' in localStorage) && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
    document.documentElement.classList.add('dark');
  }
</script>

HTML Structure for the Toggle

The toggle button itself can be as simple as a <button> with sun and moon icons. Show the sun icon in dark mode (to switch to light) and the moon icon in light mode (to switch to dark). Use Tailwind's hidden and block with dark: variants to swap which icon is visible based on the current mode.

<button id="theme-toggle" class="p-2 rounded-lg bg-gray-200 dark:bg-gray-700">
  <!-- Moon icon (visible in light mode) -->
  <svg id="icon-moon" class="w-5 h-5 text-gray-800 dark:hidden" fill="currentColor" viewBox="0 0 20 20">
    <path d="M17.293 13.293A8 8 0 016.707 2.707a8.001 8.001 0 1010.586 10.586z" />
  </svg>
  <!-- Sun icon (visible in dark mode) -->
  <svg id="icon-sun" class="w-5 h-5 text-yellow-400 hidden dark:block" fill="currentColor" viewBox="0 0 20 20">
    <path d="M10 2a1 1 0 100 2 1 1 0 000-2zm0 14a1 1 0 100 2 1 1 0 000-2z" />
  </svg>
</button>

Writing the Toggle JavaScript

The toggle function checks whether the dark class is currently present on <html>. If it is, the function removes it and saves 'light' to localStorage. If it is not, the function adds it and saves 'dark'. This pattern is clean, reversible, and works without any external libraries or frameworks.

const toggle = document.getElementById('theme-toggle');

toggle.addEventListener('click', () => {
  const html = document.documentElement;

  if (html.classList.contains('dark')) {
    html.classList.remove('dark');
    localStorage.setItem('theme', 'light');
  } else {
    html.classList.add('dark');
    localStorage.setItem('theme', 'dark');
  }
});

Respecting OS Preference as Default

If the user has never interacted with your toggle, there is nothing in localStorage. In that case, you should fall back to the OS prefers-color-scheme media query. The window.matchMedia API lets you check this at runtime. If the OS is in dark mode and the user has not overridden it, apply the dark class so the initial experience matches their system setting.

function getInitialTheme() {
  const saved = localStorage.getItem('theme');
  if (saved) return saved;

  // No saved preference — use OS setting
  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
}

if (getInitialTheme() === 'dark') {
  document.documentElement.classList.add('dark');
}

Full Toggle Implementation

Putting it all together: the inline head script handles initial load without flash, the button HTML uses dark: variants to swap icons, and the click handler toggles the class and saves to localStorage. This complete pattern is the standard approach used by most Tailwind-based apps. It requires no dependencies and works in any environment.

<!-- In <head> (anti-flash) -->
<script>
  const saved = localStorage.getItem('theme');
  const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
  if (saved === 'dark' || (!saved && prefersDark)) {
    document.documentElement.classList.add('dark');
  }
</script>

<!-- In body JS -->
<script>
  document.getElementById('theme-toggle').addEventListener('click', () => {
    const isDark = document.documentElement.classList.toggle('dark');
    localStorage.setItem('theme', isDark ? 'dark' : 'light');
  });
</script>

Toggle Button With Smooth Transition

Add a satisfying animation to the theme switch by putting a transition-colors class on your body or root container. This makes all color changes animate smoothly instead of snapping instantly. Keep the transition duration short — around 200-300ms — to feel responsive. Apply it at the highest container level so all child elements inherit the smooth transition behavior.

<body class="bg-white dark:bg-gray-900 text-gray-900 dark:text-gray-100 transition-colors duration-200">
  <!-- All children now transition smoothly between light and dark -->
</body>

Toggle in a React Component

In React, manage the dark mode state with useState and synchronize it with the DOM and localStorage using useEffect. A common pattern is a custom useDarkMode hook that encapsulates all the logic. Trigger the DOM class change inside the effect so it stays in sync with the React state.

import { useState, useEffect } from 'react';

function useDarkMode() {
  const [dark, setDark] = useState(() => localStorage.getItem('theme') === 'dark');

  useEffect(() => {
    document.documentElement.classList.toggle('dark', dark);
    localStorage.setItem('theme', dark ? 'dark' : 'light');
  }, [dark]);

  return [dark, setDark];
}

Toggle in a Next.js App

In Next.js, the anti-flash script cannot be easily placed in <head> via a component because React hydration runs after the HTML is parsed. The recommended approach is to add the inline script via next/script with strategy='beforeInteractive', or to place it directly in a custom _document.js file inside the Head component. This ensures the script runs synchronously before the page renders.

// pages/_document.js (Next.js Pages Router)
import { Html, Head, Main, NextScript } from 'next/document';

export default function Document() {
  return (
    <Html>
      <Head>
        <script dangerouslySetInnerHTML={{ __html: `
          const t = localStorage.getItem('theme');
          const d = window.matchMedia('(prefers-color-scheme: dark)').matches;
          if (t === 'dark' || (!t && d)) document.documentElement.classList.add('dark');
        ` }} />
      </Head>
      <body><Main /><NextScript /></body>
    </Html>
  );
}

Listening to OS Changes at Runtime

Users sometimes change their OS theme while your app is open. You can listen for these changes using window.matchMedia's change event. Only apply the OS preference change if the user has not set an explicit preference in your app — otherwise you would override their in-app choice. This provides the most respectful user experience.

const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');

mediaQuery.addEventListener('change', (e) => {
  // Only auto-update if the user hasn't set an explicit preference
  if (!localStorage.getItem('theme')) {
    document.documentElement.classList.toggle('dark', e.matches);
  }
});

Toggle Accessibility Considerations

The dark mode toggle button should be keyboard accessible and have a meaningful aria-label that updates to reflect the current action. Use aria-pressed to communicate the current state to screen readers. Since only a visual icon changes, screen reader users need the label to understand what pressing the button will do.

<button
  id="theme-toggle"
  aria-label="Switch to dark mode"
  aria-pressed="false"
  class="p-2 rounded-lg bg-gray-200 dark:bg-gray-700"
>
  <!-- icons -->
</button>

<script>
  const btn = document.getElementById('theme-toggle');
  btn.addEventListener('click', () => {
    const isDark = document.documentElement.classList.toggle('dark');
    btn.setAttribute('aria-pressed', isDark);
    btn.setAttribute('aria-label', isDark ? 'Switch to light mode' : 'Switch to dark mode');
    localStorage.setItem('theme', isDark ? 'dark' : 'light');
  });
</script>

Quick Check

Test your understanding of building a dark mode toggle with Tailwind CSS.

Lesson Recap

In this lesson you learned: an inline head script prevents the flash of wrong theme on page load, classList.toggle('dark') combined with localStorage creates a persistent user toggle, and matchMedia lets you respect the OS preference as a default when no user preference is saved. Next up we apply dark mode to complex components like cards, navbars, and modals.

Perguntas Frequentes

A aula “Criação de um alternador do modo escuro” é grátis?

Sim — o texto completo de “Criação de um alternador do modo escuro” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de Tailwind CSS Academy, atualize para CoddyKit PRO. O curso de Tailwind CSS Academy inclui 4 aulas no total.

O que vou aprender em “Criação de um alternador do modo escuro”?

Implemente um alternador em JavaScript que adicione e remova a classe dark do elemento html e persista a preferência em localStorage. Você pratica Tailwind CSS Academy com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar Tailwind CSS Academy?

Nenhuma experiência prévia é necessária. Tailwind CSS Academy no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 3 de 4.

Quanto tempo leva a aula “Criação de um alternador do modo escuro”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de Tailwind CSS Academy?

Sim. Cada aula de Tailwind CSS Academy inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

  1. Estratégias para o modo escuro
  2. Aplicação de variantes escuras
  3. Criação de um alternador do modo escuro
  4. Modo escuro para componentes complexos
← Voltar para Tailwind CSS Academy