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Last updated: May 18, 2024, 5:49 a.m.

HTML Head

HTML Body

<h1>Navigation Menu Button: Keyboard Support</h1>
    <div class="menu-button-links">
      <button type="button">
        WAI-ARIA Quick Links
        <svg xmlns="http://www.w3.org/2000/svg"
             class="down"
             width="12"
             height="9"
             viewBox="0 0 12 9">
          <polygon points="1 0, 11 0, 6 8"></polygon>
        </svg>
      </button>
      <ul class="menu">
        <li>
          <a href="https://www.w3.org/">
            W3C Home Page
          </a>
        </li>
        <li>
          <a href="https://www.w3.org/standards/webdesign/accessibility">
            W3C Web Accessibility Initiative
          </a>
        </li>
        <li>
          <a href="https://www.w3.org/TR/wai-aria/">
            ARIA Specification
          </a>
        </li>
        <li>
          <a href="https://w3c.github.io/aria-practices/">
            Authoring Practices
          </a>
        </li>
        <li>
          <a href="https://www.w3.org/TR/html-aria/#el-li">
            HTML Accessibility API Mappings
          </a>
        </li>
        <li>
          <a href="https://w3c.github.io/core-aam/#mapping_role">
            Core ARIA Accessibility API Mappings
          </a>
        </li>
        <li>
          <a href="https://www.w3.org/TR/accname-aam-1.1/">
            Accessible Name and Description
          </a>
        </li>
      </ul>
    </div>

<h2>Accessibility Feature</h2>
    <p>Includes keyboard support required by the menu button design pattern:
    <ul>
    <li>
       Button opens menu moves keyboard focus to a menu option.
       <ul>
          <li><kbd>Space</kbd></li>
          <li><kbd>Enter</kbd>
          </li>
          <li>
             <kbd>Up arrow</kbd>
          </li>
          <li>
             <kbd>Down arrow</kbd>
          </li>
       </ul>
    </li>
    <li>
       Move through menu options with cursor keys.
       <ul>
          <li>
             <kbd>Up arrow</kbd>
          </li>
          <li>
             <kbd>Down arrow</kbd>
          </li>
          <li>
             <kbd>Home</kbd>
          </li>
          <li>
             <kbd>End</kbd>
          </li>
       </ul>
    </li>
    <li>Move through menu options with first letter keys.</li>
    <ul>
       <li>
          <kbd>A-Z</kbd>
       </li>
       <li>
          <kbd>a-z</kbd>
       </li>
    </ul>
    <li>
       Close menu and move focus back to button.
       <ul>
          <li>
             <kbd>Escape</kbd>
          </li>
       </ul>
     </li>
    </ul>
   <h2>Accessibility Issues</h2>
    <ul>
      <li>No description of behaviors to assistive technologies.</li>
      <li>Poor keyboard focus styling.</li>
    </ul>

CSS

JavaScript

class MenuButtonLinks {

constructor(domNode) {

this.domNode       = domNode;
    this.buttonNode    = domNode.querySelector('button');
    this.menuNode      = domNode.querySelector('.menu');
    this.menuitemNodes = []
    this.firstMenuitem = false;
    this.lastMenuitem  = false;
    this.firstChars = [];

this.buttonNode.addEventListener('keydown', this.onButtonKeydown.bind(this));
    this.buttonNode.addEventListener('click', this.onButtonClick.bind(this));

var nodes = this.menuNode.querySelectorAll('a');

for (var i = 0; i < nodes.length; i++) {
      var menuitem = nodes[i];
      this.menuitemNodes.push(menuitem);
      menuitem.tabIndex = -1;
      this.firstChars.push(menuitem.textContent.trim()[0].toLowerCase());

menuitem.addEventListener('keydown', this.onMenuitemKeydown.bind(this));

menuitem.addEventListener('mouseover', this.onMenuitemMouseover.bind(this));

if( !this.firstMenuitem) {
        this.firstMenuitem = menuitem;
      }
      this.lastMenuitem = menuitem;
    }

domNode.addEventListener('focusin', this.onFocusin.bind(this));
    domNode.addEventListener('focusout', this.onFocusout.bind(this));

window.addEventListener('mousedown', this.onBackgroundMousedown.bind(this), true);
  }

// Popup menu methods

openPopup() {
    var rect = this.menuNode.getBoundingClientRect();
    this.menuNode.style.display = 'block';
    this.buttonNode.classList.add('open');
  }

closePopup() {
    if (this.isOpen()) {
      this.buttonNode.classList.remove('open');
      this.menuNode.style.display = 'none';
    }
  }

isOpen() {
    return this.buttonNode.classList.contains('open');
  }

// Focus management methods

setFocusToMenuitem(newMenuitem) {
    this.menuitemNodes.forEach(function(item) {
      if (item === newMenuitem) {
        item.tabIndex = 0;
        newMenuitem.focus();
      }
      else {
        item.tabIndex = -1;
      }
    });
  }

setFocusToFirstMenuitem(currentMenuitem) {
    this.setFocusToMenuitem(this.firstMenuitem);
  }

setFocusToLastMenuitem(currentMenuitem) {
    this.setFocusToMenuitem(this.lastMenuitem);
  }

setFocusToPreviousMenuitem(currentMenuitem) {
    var newMenuitem, index;

if (currentMenuitem === this.firstMenuitem) {
      newMenuitem = this.lastMenuitem;
    }
    else {
      index = this.menuitemNodes.indexOf(currentMenuitem);
      newMenuitem = this.menuitemNodes[ index - 1 ];
    }

this.setFocusToMenuitem(newMenuitem);

return newMenuitem;
  }

setFocusToNextMenuitem(currentMenuitem) {
    var newMenuitem, index;

if (currentMenuitem === this.lastMenuitem) {
      newMenuitem = this.firstMenuitem;
    }
    else {
      index = this.menuitemNodes.indexOf(currentMenuitem);
      newMenuitem = this.menuitemNodes[ index + 1 ];
    }
    this.setFocusToMenuitem(newMenuitem);

return newMenuitem;
  }

setFocusByFirstCharacter(currentMenuitem, char) {
    var start, index;

if (char.length > 1) {
      return;
    }

char = char.toLowerCase();

// Get start index for search based on position of currentItem
    start = this.menuitemNodes.indexOf(currentMenuitem) + 1;
    if (start >=  this.menuitemNodes.length) {
      start = 0;
    }

// Check remaining slots in the menu
    index = this.firstChars.indexOf(char, start);

// If not found in remaining slots, check from beginning
    if (index === -1) {
      index = this.firstChars.indexOf(char, 0);
    }

// If match was found...
    if (index > -1) {
      this.setFocusToMenuitem(this.menuitemNodes[index]);
    }
  }

// Utilities

getIndexFirstChars(startIndex, char) {
    for (var i = startIndex; i < this.firstChars.length; i++) {
      if (char === this.firstChars[i]) {
        return i;
      }
    }
    return -1;
  }

// Menu event handlers

onFocusin(event) {
    this.domNode.classList.add('focus');
  }

onFocusout(event) {
    this.domNode.classList.remove('focus');
  }

onButtonKeydown(event) {
    var tgt = event.currentTarget,
      key = event.key,
      flag = false;

switch (key) {
      case ' ':
      case 'Enter':
      case 'ArrowDown':
      case 'Down':
        this.openPopup();
        this.setFocusToFirstMenuitem();
        flag = true;
       break;

case 'Esc':
      case 'Escape':
          this.closePopup();
          this.buttonNode.focus();
          flag = true;
        break;

case 'Up':
      case 'ArrowUp':
        this.openPopup();
        this.setFocusToLastMenuitem();
        flag = true;
        break;

default:
        break;
    }

if (flag) {
      event.stopPropagation();
      event.preventDefault();
    }
  }

onButtonClick(event) {
    if (this.isOpen()) {
      this.closePopup();
      this.buttonNode.focus();
    }
    else {
      this.openPopup();
      this.setFocusToFirstMenuitem();
    }

event.stopPropagation();
    event.preventDefault();
  }

onMenuitemKeydown(event) {
    var tgt = event.currentTarget,
      key = event.key,
      flag = false;

function isPrintableCharacter (str) {
      return str.length === 1 && str.match(/\S/);
    }

if (event.ctrlKey || event.altKey  || event.metaKey) {
      return;
    }

if (event.shiftKey) {
      if (isPrintableCharacter(key)) {
        this.setFocusByFirstCharacter(tgt, key);
        flag = true;
      }

if (event.key === 'Tab') {
        this.buttonNode.focus();
        this.closePopup();
        flag = true;
      }
    }
    else {

switch (key) {
        case ' ':
         window.location.href=tgt.href;
         break;

case 'Esc':
        case 'Escape':
          this.closePopup();
          this.buttonNode.focus();
          flag = true;
          break;

case 'Up':
        case 'ArrowUp':
          this.setFocusToPreviousMenuitem(tgt);
          flag = true;
          break;

case 'ArrowDown':
        case 'Down':
          this.setFocusToNextMenuitem(tgt);
          flag = true;
          break;

case 'Home':
        case 'PageUp':
          this.setFocusToFirstMenuitem();
          flag = true;
          break;

case 'End':
        case 'PageDown':
          this.setFocusToLastMenuitem();
          flag = true;
          break;

case 'Tab':
          this.closePopup();
          break;

default:
          if (isPrintableCharacter(key)) {
            this.setFocusByFirstCharacter(tgt, key);
            flag = true;
          }
          break;
      }

}

if (flag) {
      event.stopPropagation();
      event.preventDefault();
    }
  }

onMenuitemMouseover(event) {
    var tgt = event.currentTarget;
    tgt.focus();
  }

onBackgroundMousedown(event) {
    if (!this.domNode.contains(event.target)) {
      if (this.isOpen()) {
        this.closePopup();
        this.buttonNode.focus();
      }
    }
  }
}

// Initialize navigation menu buttons

window.addEventListener('load', function () {
  var menuButtons = document.querySelectorAll('.menu-button-links');
  for(var i=0; i < menuButtons.length; i++) {
    var menuButton = new MenuButtonLinks(menuButtons[i]);
  }
});