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HTML

CSS

CSS Base

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JavaScript

Babel includes JSX processing.

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HTML

              
                <p>Just a simple example.</p>
<nav role="navigation">
  <ul>
    <li><a href="#">Home</a></li>
    <li><a href="#">Shop</a></li>
    <li>
        <span class="topItem">Space Bears</span>			
      <ul>
        <li><a href="#">Space Bear 6</a></li>
        <li><a href="#">Space Bear 6 Plus</a></li>
      </ul>
    </li>
    <li>
      <span class="topItem">Space Bunnies</span>
      <ul>
        <li><a href="#">Space Bunnies Deluxe</a></li>
        <li><a href="#">Space Bunnies Vintage Edition</a></li>
      </ul>
    </li>
    <li><a href="#">Mars Cars</a></li>
    <li><a href="#">Contact</a></li>
  </ul>
</nav>
              
            
!

CSS

              
                nav button {
  font-family: Times, serif;
  border: none;
  font-size: 1em;
  background: transparent;
  padding: 0;
}
button[aria-expanded]::after {
  content: "+";
}
button[aria-expanded="true"]::after {
  content: "-";
}
/* note: use background images preferably. Generated content is read by some screen readers; used here for simplicity only */

              
            
!

JS

              
                var expandableTopItems = document.querySelectorAll(".topItem"); 

expandableTopItems.forEach(function(topItem) {
   /* buttons are generated on init, to support no JS and have the submenus displayed by default */
  topItem.innerHTML=`<button type=button aria-expanded="false">${topItem.textContent}</button>`; //insert a button in the spans
  topItem.nextElementSibling.hidden=true; //hide submenu by default
  var btn=topItem.firstElementChild;
  /* add listener on each button to implement the behavior on click */
  btn.addEventListener("click", function(e) {
    let expanded = this.getAttribute("aria-expanded") === "true" || false;
    this.setAttribute("aria-expanded", !expanded);
    let submenu = this.parentNode.nextElementSibling;
    submenu.hidden = !submenu.hidden;
    e.preventDefault();
    return false;
  });
});

              
            
!
999px

Console