Toggle light and dark themes in Bootstrap - DEV

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In this article we will learn how we can easily toggle between light and dark theme.

While theming in Bootstrap[1] can be done through it's built-in SASS variables, for this article we are going to use provided css stylesheets.

Bootswatch[2] has some great themes, we're going to use it's Cyborg[3] theme for darker variant. And for light, we are going to use Bootstrap's default theme.

So, let's get started.

Create project folder and index.html file 

mkdir toggle-bootstrap-theme cd toggle-bootstrap-theme

Create the index.html file in it:

<!DOCTYPE html> <html lang="en">   <head>     <!-- Required meta tags -->     <meta charset="utf-8" />     <meta       name="viewport"       content="width=device-width, initial-scale=1, shrink-to-fit=no"     />      <!-- Bootstrap CSS -->     <link       rel="stylesheet"       href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css"       integrity="sha384-JcKb8q3iqJ61gNV9KGb8thSsNjpSL0n8PARn9HuZOnIxN0hoP+VmmDGMN5t9UJ0Z"       crossorigin="anonymous"     />      <!-- ๐Ÿšจ Notice this link -->     <link id="dark-theme-style" rel="stylesheet" />      <title>Toggle Bootstrap Theme</title>   </head>   <body>     <nav class="navbar navbar-transparent">       <!-- ๐Ÿšจ Notice the toggleTheme() function -->       <a         href="javascript:void()"         class="btn btn-outline-info btn-lg ml-auto font-weight-bold"         id="theme-toggler"         onclick="toggleTheme()"       ></a>     </nav>      <div class="container-fluid">       <div class="jumbotron">         <h1 class="display-4">Hello, world!</h1>         <p class="lead">           This is a simple hero unit, a simple jumbotron-style component for           calling extra attention to featured content or information.         </p>         <hr class="my-4" />         <p>           It uses utility classes for typography and spacing to space content           out within the larger container.         </p>         <a class="btn btn-primary btn-lg" href="#" role="button">Learn more</a>       </div>     </div>      <!-- Optional JavaScript -->     <!-- jQuery first, then Popper.js, then Bootstrap JS -->     <script       src="https://code.jquery.com/jquery-3.5.1.slim.min.js"       integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj"       crossorigin="anonymous"     ></script>     <script       src="https://cdn.jsdelivr.net/npm/popper.js@1.16.1/dist/umd/popper.min.js"       integrity="sha384-9/reFTGAW83EW2RDu2S0VKaIzap3H66lZH81PoYlFhbGU+6BZp6G7niu735Sk7lN"       crossorigin="anonymous"     ></script>     <script       src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"       integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV"       crossorigin="anonymous"     ></script>      <!-- ๐Ÿšจ Our custom JavaScript  -->     <script src="index.js"></script>   </body> </html>

Notice these 2 snippet in above code:

<link> to dynamically load stylesheet 

<link id="dark-theme-style" rel="stylesheet" />

Here, we will render dark theme stylesheet through JavaScript. Also note that we have kept this after our default stylesheet, so that if any rules is missing in dark one, it will be taken from default.

<a> to toggle themes 

<a         href="javascript:void()"         class="btn btn-outline-info btn-lg ml-auto font-weight-bold"         id="theme-toggler"         onclick="toggleTheme()" ></a>

This anchor tag will help user to toggle between light and dark theme. We are going to create function toggleDark in JavaScript. Let's see that.

Create index.js file 

// you can use app's unique identifier here const LOCAL_STORAGE_KEY = "toggle-bootstrap-theme";  const LOCAL_META_DATA = JSON.parse(localStorage.getItem(LOCAL_STORAGE_KEY));  // you can change this url as needed const DARK_THEME_PATH = "https://bootswatch.com/4/cyborg/bootstrap.min.css";  const DARK_STYLE_LINK = document.getElementById("dark-theme-style"); const THEME_TOGGLER = document.getElementById("theme-toggler");  let isDark = LOCAL_META_DATA && LOCAL_META_DATA.isDark;  // check if user has already selected dark theme earlier if (isDark) {   enableDarkTheme(); } else {   disableDarkTheme(); }   /**  * Apart from toggling themes, this will also store user's theme preference in local storage.  * So when user visits next time, we can load the same theme.  *  */ function toggleTheme() {   isDark = !isDark;   if (isDark) {     enableDarkTheme();   } else {     disableDarkTheme();   }   const META = { isDark };   localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(META)); }  function enableDarkTheme() {   DARK_STYLE_LINK.setAttribute("href", DARK_THEME_PATH);   THEME_TOGGLER.innerHTML = "๐ŸŒ™ Dark"; }  function disableDarkTheme() {   DARK_STYLE_LINK.setAttribute("href", "");   THEME_TOGGLER.innerHTML = "๐ŸŒž Light"; }

I believe that above code is self-explanatory ๐Ÿ˜‰ and no further explanation is required.

Output

After successfully writing all of the above code, you can simply open index.html in browser to see the output:

Toggle Bootstrap Theme output

๐Ÿ‘‰ The http call to dark stylesheet is done only once per session. If user switches back to light theme and then again dark theme, it is loaded from cache. See the Network panel in browser devtools to see this.

Conclusion

We learned how easily we can toggle between light and dark theme with just few lines of JavaScript code.

If you're looking for a complete Bootstrap theme generation code base with support of sass, gulp, auto-refresh, etc. checkout my github repo:

Quickly generate and showcase your bootstrap theme.

Bootstrap Theme Kit

Quickly โšก Generate and Showcase ๐ŸŽฏ your bootstrap theme ๐ŸŽจ. Get Started[4] or See sample theme[5].

GitHub license Commitizen friendly

๐Ÿš€ Getting Started

โ˜‘๏ธ Minimum Requirements

node -v // v10.17.0 git --version // git version 2.x

โฌ‡๏ธ Steps to Follow

  1. First, fork this repo.
  2. Open terminal and:
git clone <forked-repo-url> cd bootstrap-theme-kit npm i npm run init npm start
  1. Browser will open at 3000 port.
  2. Start editing your scss/html files and browser will reload.

๐Ÿ† Features

And yes, always believe in yourself...

silhouette of trees under starry night photo โ€“ Free Nature Image on Unsplash

Photo by Nick Dunlap on Unsplash[6][7]

References

  1. ^ theming in Bootstrap (getbootstrap.com)
  2. ^ Bootswatch (bootswatch.com)
  3. ^ Cyborg (bootswatch.com)
  4. ^ Get Started (raw.githubusercontent.com)
  5. ^ See sample theme (shhdharmen.github.io)
  6. ^ Nick Dunlap (unsplash.com)
  7. ^ Unsplash (unsplash.com)
keywords bootstrap, css3, javascript, webdev, software, coding, development, engineering, inclusive, community

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