Simple Responsive Modal Window In Pure JavaScript

A minimal JavaScript library that enables you to show a responsive modal window on the html page.

How to use it:

Create the modal window that is hidden on page load.

<div class="modal-wrap" id="modal-demo">
  <div class="modal-container">
    <div class="modal-header">
      <h2 class="modal-title">Modal Title</h2>
      <button class="close-modal">&times;</button>
    </div>
    <div class="modal-content">
      <h3>Modal inner heading tag H3</h3>
      <p>Lorem ipsum dolor sit amet consectetur, adipisicing elit. Molestiae itaque quaerat animi praesentium accusamus
        expedita rerum unde ipsum nihil est officia, quisquam sunt reiciendis, omnis placeat distinctio similique
        illum minus.</p>
      <p>Lorem ipsum dolor sit amet consectetur, adipisicing elit. Molestiae itaque quaerat animi praesentium accusamus
        expedita rerum unde ipsum nihil est officia, quisquam sunt reiciendis, omnis placeat distinctio similique
        illum minus.</p>
    </div>
    <div class="modal-footer">
      <p>Modal footer</p>
    </div>
  </div>
</div>

The CSS styles for the modal.

.modal-wrap {
  background: rgba(0, 0, 0, 0.7);
  height: 100%;
  left: 0;
  opacity: 0;
  overflow: auto;
  position: fixed;
  top: 0;
  visibility: hidden;
  width: 100%;
  z-index: 10;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  justify-content: center;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-transition: all 0.3s ease-in-out;
  transition: all 0.3s ease-in-out;
}
.modal-wrap.visible {
  opacity: 1;
  visibility: visible;
}
.modal-wrap .modal-container {
  background: #fff;
  margin: 1em;
  max-width: 100%;
  width: 600px;
  z-index: 100;
}
.modal-wrap .modal-container .modal-header,  .modal-wrap .modal-container .modal-footer {
  background: #000;
  float: left;
  width: 100%;
}
.modal-wrap .modal-header .modal-title {
  color: #fff;
  float: left;
  font-size: 2em;
  margin: 0;
  padding: 15px 30px;
}
.modal-wrap .modal-header .close-modal {
  background: transparent;
  border: 0;
  color: #fff;
  cursor: pointer;
  float: right;
  font-size: 40px;
  opacity: 0.4;
  -webkit-transition: all 0.3s ease-in-out;
  transition: all 0.3s ease-in-out;
}
.modal-wrap .modal-header .close-modal:hover { opacity: 1; }
.modal-wrap .modal-content {
  float: left;
  margin: 0;
  padding: 15px 30px;
  width: 100%;
}
.modal-wrap .modal-content p:last-child { margin-bottom: 0; }
.modal-wrap .modal-footer { text-align: center; }
.modal-wrap .modal-footer p {
  color: #ccc;
  font-size: 12px;
  font-style: italic;
  margin: 10px;
}
.modal-wrap .modal-footer a { color: #fff; }

Create a toggle button to open the modal window.

<button id="open-modal" class="triger-modal" data-triger="modal-demo">Open Modal</button>

The main JavaScript.

// Modal button
var openModal = document.getElementById('open-modal');
// Modal ID
var modal = document.getElementById('modal-demo');
// Close modal button
var closeModal = document.getElementsByClassName('close-modal')[0];
// Open modal event listener
openModal.addEventListener('click', function(){
    modal.classList.toggle('visible');
});
// Close modal event listener
closeModal.addEventListener('click', function(){
    modal.classList.remove('visible');
});