Creating Popup Dropdowns with JavaScript and CSS3

An animated and touch-enabled dropdown component that uses CSS3 transforms and transitions to popup a dropdown list as you click on the toggle button.

How to use it:

Create a dropdown list with a toggle link on your web page.

<div class="dropdown">
  <a href="#" class="btn">
    Dropdown
  </a>
  <div class="outer-list">
    <ul>
      <li>List item 1</li>
      <li>List item 2</li>
      <li>List item 3</li>
      <li>List item 4</li>
    </ul>
  </div>
</div>

The core CSS / CSS3 styles for the dropdown list.

.dropdown {
  position: relative;
  margin: 0 auto;
  width: 15em;
}
.dropdown > .outer-list {
  position: absolute;
  z-index: 1;
  top: 0;
  left: 0;
  height: 100%;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  transform: scale(0);
  opacity: 0;
  visibility: hidden;
  transition: all 0.35s ease;
}
.dropdown > .outer-list.top {
  align-items: flex-start;
  transform-origin: 50% 0;
}
.dropdown > .outer-list.left { justify-content: flex-start; }
.dropdown > .outer-list.bottom {
  align-items: flex-end;
  transform-origin: 50% 100%;
}
.dropdown > .outer-list.right { justify-content: flex-end; }
.dropdown > .outer-list > ul {
  list-style: none;
  padding: 0;
  text-align: center;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  background: rgba(255, 255, 255, 0.95);
  box-shadow: 0 0 2px 1px rgba(0, 0, 0, 0.1);
  border-radius: .2em;
}
.dropdown > .outer-list > ul li {
  padding: .25em 3em;
  margin: .25em;
  width: 100%;
  cursor: pointer;
  transition: background 0.35s ease;
}
.dropdown > .outer-list > ul li:hover { background: rgba(0, 0, 0, 0.07); }

Style the toggle button.

.btn {
  position: relative;
  display: block;
  width: 100%;
  text-align: center;
  background: #03A9F4;
  color: #fff;
  padding: 1em;
  border-radius: .15em;
  cursor: pointer;
  transition: all 0.35s ease;
  overflow: hidden;
}
.btn:after {
  content: '';
  position: absolute;
  bottom: -50%;
  right: -50%;
  z-index: 1;
  overflow: hidden;
  width: 0;
  height: 0;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.35);
  transition: all 0.35s ease;
}
.btn:active:after,
.btn.dropdown-open:after {
  width: 200%;
  height: 200%;
}
.btn:hover { box-shadow: inset 0 0 40px rgba(0, 0, 0, 0.1); }
.btn.dropdown-open + .outer-list {
  transform: scale(1);
  opacity: 1;
  visibility: visible;
}

The JavaScript to active the dropdown list and enable touch support.

'use strict';
(function() {
  var _btns = document.querySelectorAll('.btn'),
    _eachBtn = function(callback) {
      Array.prototype.forEach.call(_btns, function(elem) {
        callback.call(this, elem);
      });
    },
    _initListener = function(e) {
      e.preventDefault();
      e.stopPropagation();
      _eachBtn(function(btn) {
        btn.classList.remove('dropdown-open')
      });
      this.classList.toggle('dropdown-open');
    },
    _hideAll = function() {
      _eachBtn(function(btn) {
        btn.classList.remove('dropdown-open');
      });
    };
  _eachBtn(function(btn) {
    btn.addEventListener('touchend', function(e) {
      _initListener.call(this, e);
    });
    btn.addEventListener('click', function(e) {
      _initListener.call(this, e);
    });
  });
  document.addEventListener('touchend', function() {
    _hideAll();
  });
  
  document.addEventListener('click', function() {
    _hideAll();
  });
})();