Pen Settings

HTML

About HTML Preprocessors

HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

Learn more · Versions

Adding Classes

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

!
Insecure Resource

The resource you are linking to is using the 'http' protocol, which may not work when the browser is using https.

CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

Learn more · Versions

CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

Add External Stylesheets/Pens

Any URLs added here will be added as <link>s in order, and before the CSS in the editor. You can use the CSS from another Pen by using its URL and the proper URL extension.

Powered by Algolia
About External Resources

You can apply CSS to your Pen from any stylesheet on the web. Just put a URL to it here and we'll apply it, in the order you have them, before the CSS in the Pen itself.

You can also link to another Pen here (use the .css URL Extension) and we'll pull the CSS from that Pen and include it. If it's using a matching preprocessor, use the appropriate URL Extension and we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

Learn more

+ add another resource

JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

Learn more · Versions

Babel includes JSX processing.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

Powered by Algolia
About External Resources

You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

Learn more

+ add another resource

Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

Powered by Algolia
About Packages

Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

All packages are different, so refer to their docs for how they work.

If you're using React / ReactDOM, make sure to turn on Babel for the JSX processing.

Behavior

Auto Save

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

Want to change your Syntax Highlighting theme, Fonts and more?

Visit your global Editor Settings.

HTML 

              
                <section id="menu" class="tab-menu">
  <div>
    <b>Javascript Tabbed Menu</b>
    <a href="#menu" data-click-switch="menu about selected" class="menu about tab-index selected">about</a>
    <a href="#menu" data-click-switch="menu city-menu selected" class="menu city-menu tab-index">cities</a>
    <a href="#menu" data-click-switch="menu fruit-menu selected" class="menu fruit-menu tab-index">fruit</a>
    <a href="#menu" data-click-switch="menu animal-menu selected" class="menu animal-menu tab-index">animals</a>
  </div>
</section>
<section id="cities" class="menu city-menu tab-content">
  <div class="tab-menu">
    <b>Cities:</b>
    <a href="#cities" data-click-switch="cities atl selected" class="cities atl tab-index selected">atlanta*</a>
    <a href="#cities" data-click-switch="cities nyc selected" class="cities nyc tab-index">new york</a>
    <a href="#cities" data-click-switch="cities la selected" class="cities la tab-index">los angeles</a>
  </div>  
  <div data-hover-switch="atl-hover selected" class="cities atl tab-content selected">
    <h2>Atlanta</h2>
    <img src="https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcRamIa4IbpbIEho_cgrp2kU0a7IBY3sguNxUULzBd5IDY9tbIzwcg">
    <div class="atl-hover tab-content"><h3>Atlanta is the best!</h3></div>
  </div>
  <div class="cities nyc tab-content">
    <h2>New York</h2>
    <img src="http://www.nyhabitat.com/images-layout/temp_newyork.jpg">
  </div>
  <div class="cities la tab-content">
    <h2>Las Angeles</h2>
    <img src="https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQLSk4-uA8IpWWhT3te-MfGGFYAJ2zcKER9_63zMs6FIO2_MPlN">
  </div>
  
</section>
<section id="fruit" class="menu fruit-menu tab-content">
  <div class="tab-menu">
    <b>Fruit:</b>
    <a href="#fruit" data-click-switch="fruit apple selected" class="fruit apple tab-index selected">apple</a>
    <a href="#fruit" data-click-switch="fruit banana selected" class="fruit banana tab-index">banana*</a>
    <a href="#fruit" data-click-switch="fruit pear selected" class="fruit pear tab-index">pear</a>
  </div>
  <div class="fruit apple tab-content selected">
    <h2>Apples</h2>
    <img src="https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcRC3wZDxYZG1euB7Xgp7rY88MxPsCvs2s9UfDb67ncFcUMjt7a6" />
  </div>
  <div data-hover-switch="banana-hover selected" class="fruit banana tab-content">
    <h2>Bananas</h2>
    <img src="https://www.organicfacts.net/wp-content/uploads/2013/05/Banana21.jpg" />
    <div class="banana-hover tab-content"><h3>Bananas are bananas!</h3></div>
  </div>
  <div class="fruit pear tab-content">
    <h2>Pears</h2>
    <img src="https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcTKXCHA7WHLj8oITo_0Rgb4Cy_4P8bH1DXSFJ52EBSTlXZ7H6RZ4LEnsmkyuw" />
  </div>
</section>
<section id="animals" class="menu animal-menu tab-content">
  <div class="tab-menu">
    <b>Animals:</b>
    <a href="#animals" data-click-switch="animals cat selected" class="animals cat tab-index selected">cat*</a>
    <a href="#animals" data-click-switch="animals dog selected" class="animals dog tab-index">dog</a>
  </div>
  <div data-hover-switch="cat-hover selected" class="animals cat tab-content selected">
    <h2>Cats</h2>
    <img src="https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSn8YEWhbyMuoOIv-hkDABdhEqFU565HVuElyIhgjZ0seS85pRJExcWDns" />
    <div class="cat-hover tab-content"><h3>Meows!</h3></div>
  </div>
  <div class="animals dog tab-content">
    <h2>Dogs</h2>
    <img src="https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcRTZc2-aCFM0MTmm9v-vF20ZJn8rT2tOmH9uaB5h5yOyOokeRMZ" />
  </div>
</section>
<section id="about" class="menu about tab-content selected">
  <p>
    A quick tabbing system created via javascript.
    Use the attribute <code>data-switch="fruit apple selected"</code> to select the apple fruit tab.
    <br><br>
    When clicking on the switch for apple, the script will:
    <ol>
      <li>remove the class-name <code>selected</code> from all elements containing the class <code>fruit</code>.</li>
      <li>Then, the script will add the class-name <code>selected</code> to all elements containing the class <code>apple</code>.</li>
      <li>Finally, with proper use of CSS, this tabbed menu system is functional</li>
    </ol>
    The events are attached to the document, so additional tabs can be created on the fly without "rewiring" events.
  </p>  
</section>
!

CSS 

              
                * {box-sizing: border-box;}

body {font-family: sans-serif; margin: 2em auto; width: 90%; min-width: 320px;}

code {background-color: lightgrey; color: green}
#menu {margin-bottom: 2em;}
#menu div {margin-bottom: 0em; display: inline-block; width: 584px;}

.tab-menu {padding-bottom: 0.25em; border-bottom: solid 2px lightgrey; text-align: left;}
.menu b {margin-right: 2em;}

.tab-index {
  border-bottom: solid 2px clear;
  text-decoration: none;
  color: lightgrey;
  padding: 0.25em 1em;
  letter-spacing: -1px;
  transition: letter-spacing 0.25s ease, color 1s ease, border-color 2s ease;
  text-transform: lowercase;
}
.tab-index:hover {
  opacity: 0.25;
  color: green;
  /* border-bottom: solid 2px green; */
  /* text-shadow: 0px 1px 1px rgba(0,0,0,0.25); */
}
.tab-index.selected {
  text-shadow: 0px 1px 1px rgba(0,0,0,0.1);
  border-bottom: solid 2px green; 
  color: green; 
  font-weight: bold; 
  letter-spacing: 2px;
  text-transform: capitalize;
}


.tab-content {padding: 0em; margin: 0em auto 3em auto; text-align: center;}
.tab-content:not(.selected) {display: none;}

img {height: 200px; border-radius: 50%;}

section#about {text-align: left;}
!

JS 

              
                // Helper Functions
util = {
  on: function(source, action, target, callback) {
    var fn;

    // target is given. Attach listener to source and look for target.   
    if (arguments.length > 3) {
      fn = function(e)  {
        // Ensure correct event parameter for older browsers.
        e = e ? e : window.event;

        // Create list of possible targets.
        var targets = source.querySelectorAll(target);

        // Only execute function if the event target matches the target query.
        for (var i = 0, len = targets.length; i < len; i++) if (e.target === targets[i]) return callback(e, source);

        return null;
      }
    }

    // no target is given.
    else fn = function(e) {return target(e, source)};    

    // attach events
    var actions = action.split(' ');
    for (var i = 0, len = actions.length; i < len; i++) {
      // Mozilla, Netscape, Firefox
      if (window.addEventListener) source.addEventListener(actions[i], fn, false);
      // IE
      else if (window.attachEvent) source.attachEvent('on' + actions[i], fn);
      // Fail Safe
      else source['on' + actions[i]] = fn;
    }
    return fn;    
  },
  
  separate: function(text, delimiter, spaces) {return text.trim().split(new RegExp('[' + ((delimiter || ',;\\s') + (delimiter && spaces ? '\\s' : '')) + ']+'))},
  
  hasClass: function(e, c) {return !!e.className.match(new RegExp('(\\s|^)' + c + '(\\s|$)'))},

  addClass: function(e, c) {if (!util.hasClass(e, c)) e.className += ' ' + c},

  removeClass: function(e, c) {
    if (util.hasClass(e, c)) {
      var reg = new RegExp('(\\s|^)' + c + '(\\s|$)');
      e.className = e.className.replace(reg, ' ');
    }
  }
}

function initSwitches() {
  
  // Event handler for clicking a switch.
  function clickHandler(evt) {
    var attr = util.separate(evt.target.getAttribute('data-click-switch')); // group, target, class
    if (attr.length > 2) {  
      // Turn off all in group.
      var group = document.getElementsByClassName(attr[0]);
      for (var i = 0, len = group.length; i < len; i++) util.removeClass(group[i], attr[2]);
      // Turn on all targets.
      var target = document.getElementsByClassName(attr[1]);
      for (var i = 0, len = target.length; i < len; i++) util.addClass(target[i], attr[2]);
      // Do not follow links.
      evt.preventDefault();
    }
  }
  
  // Event handler for hovering over a switch.
  function hoverHandler(evt) {
    var attr = util.separate(evt.target.getAttribute('data-hover-switch')); // target, class
    if (attr.length > 1) {
      var targets = document.getElementsByClassName(attr[0]);
      // Turn on all in group
      if (evt.type == 'mouseenter') for (var i = 0, len = targets.length; i < len; i++) util.addClass(targets[i], attr[1]);      
      // Turn off all in group
      if (evt.type == 'mouseleave') for (var i = 0, len = targets.length; i < len; i++) util.removeClass(targets[i], attr[1]);
    }
  }
  
  // Add an event to all switches.
  var switches;
  switches = document.querySelectorAll('[data-click-switch]');
  if (switches) for (var i = 0, len = switches.length; i < len; i++) util.on(switches[i], 'click', clickHandler);
  switches = document.querySelectorAll('[data-hover-switch]');
  if (switches) for (var i = 0, len = switches.length; i < len; i++) util.on(switches[i], 'mouseenter mouseleave', hoverHandler);
  
}

initSwitches();

// data-switch="click fruit apple selected; hover fruit-hover apple-hover selected"
!
999px

Console