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JavaScript

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HTML 

              
                <body>
  <h1>Toggle Menu with the Animation API (Javascript)</h1>
  <p>The Animation API is an experimental Web API that provides animation controls, keyframes and a timeline to a DOM element or source.</p>
  <header>
  <div class="item--logo-wrapper">
    <div class="item item--logo">My website</div>
    <div class="item--trigger"><a href="#">Click Me</a></div>
  </div>
  <div class="item item--menu">
    <nav>
      <ul>
          <li><a href="#">Home</a></li>
          <li><a href="#">Case Studies</a></li>
          <li><a href="#">Contact</a></li>
      </ul>
    </nav>
  </div>
</header>
<footer>
  <p><a href="https://www.miguel.nz/blog/toggle-menu-with-the-animation-api/" target="_blank">Read the full article here</a</p>
</footer>
</body>
!

CSS 

              
                .item--menu {
  height: 0;
  opacity: 0;
}
 
  
// *********************************
// Only for styles purposes
// *********************************
* {
	font-family: -apple-system, BlinkMacSystemFont, sans-serif;
}

h1 {
	color: #fff;
	font-weight: normal;
	padding-top: 0.5em;
	line-height: 135%;
}
body {
	background: #10ac81;
	display: flex;
	align-items: center;
	flex-direction: column;
	max-width: 550px;
	margin: 0 auto;
	line-height: 165%;
	color: #fff;
}
header {
	width: 100%;
	margin: 0 auto;
	color: #fff;
	margin-top: 1em;
	box-shadow: 0 10px 20px -5px rgba(0,0,0,0.5);
}
footer {
	color: #f1f1f1;
	padding-top: 2em;
	font-size: 0.85em;
	position: relative;
	a {
		background: #fff;
		position: relative;
		color: #165286;
		text-decoration: none;
		display: inline-block;
		padding: 1em 2em;
		border-radius: 40px;
		&:hover {
			background: #f1f1f1;
		}
		&:active {
			top: 1px;
		}
	}
}
.item--menu {
	background: #fff;
	overflow: hidden;
	ul {
		list-style: none;
		margin: 0;
		padding: 0;
	}
	li {
		border-top: 1px solid #fff;
		border-bottom: 1px solid #ddd;
		&:last-child {
			border-bottom: 0 none;
		}
	}
	a {
		display: block;
		color: #111;
		text-decoration: none;
		padding: 1em;
	}
}
.item--logo-wrapper {
	display: flex;
	background: #165286;
	padding: 1rem;
	justify-content: space-between;
}
.item--logo {
	font-weight: bold;
	font-size: 1.2em;
}
.item--trigger {
	a {
		color: #fff;
		text-decoration: none;
		text-transform: uppercase;
		font-size: 0.85em;
	}
}
!

JS 

              
                class headerMenu { 
  constructor() {
    // The trigger and menu wrapper
    this.triggerMenu = document.querySelector('.item--trigger a');
    this.menuWrapper = document.querySelector('.item--menu');

    // The event Listener
    this.toggleMenu = this.toggleMenu.bind(this);
    this.triggerMenu.addEventListener('click', this.toggleMenu);

    // The animation
    this.openMenuAnimation = new Animation(this.menuKeyFrames({
      duration: 200, 
      fill: 'forwards' 
    }));

    this.closeMenuAnimation = new Animation(this.menuKeyFrames({
      duration: 200, 
      fill: 'forwards',
      direction: 'reverse'
    }));
  }

  menuKeyFrames(options) {
    const menuNavHeight = parseInt(this.menuWrapper.querySelector('nav').getBoundingClientRect().height);
    
    return new KeyframeEffect( 
      this.menuWrapper,
      [{ 
          height: 0,
          opacity: 0,
        },
        { 
          height: `${menuNavHeight}px`,
          opacity: 1
        }], 
      options 
    );
  }

  toggleMenu(event) {
    event.preventDefault();
    if (!this.triggerMenu.classList.contains('active')) {
      this.triggerMenu.classList.add('active');
      this.closeMenuAnimation.cancel();
      this.openMenuAnimation.play();
    } else {
      this.triggerMenu.classList.remove('active');
      this.openMenuAnimation.cancel();
      this.closeMenuAnimation.play();
    }
  }
}

new headerMenu();
!
999px

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