Simple Modal Window With Background Blur Effect

A simple, lightweight vanilla JavaScript library that lets you create a modal window while blurring the background content to focus your user’s attention on modal content.

How to use it:

The html structure for the modal window.

<div id="myModal" class="Modal is-hidden is-visuallyHidden">
  <!-- Modal content -->
  <div class="Modal-content">
    <span id="closeModal" class="Close">&times;</span>
    <p>Simple Modal</p>
  </div>
</div>

Create a toggle button to open the modal window.

<button id="myBtn">Open Modal</button>

The main CSS styles for the modal window.

.Modal {
  display: block;
  position: fixed;
  left: 0;
  top: 0;
  z-index: 9999;
  width: 100%;
  height: 100%;
  padding-top: 100px;
  background-color: black;
  background-color: rgba(0, 0, 0, 0.4);
  -webkit-transition: 0.5s;
  overflow: auto;
  transition: all 0.3s linear;
}
.Modal-content {
  background-color: #fefefe;
  margin: auto;
  padding: 20px;
  border-radius: 4px;
  max-width: 300px;
  height: 450px;
}
.ModalOpen { overflow: hidden; }
.is-hidden { display: none; }
.is-visuallyHidden { opacity: 0; }

Style and position the modal close button.

.Close {
  color: #aaaaaa;
  float: right;
  font-size: 16px;
}
.Close:hover, .Close:focus {
  color: #000;
  text-decoration: none;
  cursor: pointer;
}

Blur the main content using CSS3 filters.

.is-blurred {
  filter: blur(2px);
  -webkit-filter: blur(2px);
}

The main JavaScript.

// Get the modal
var modal = document.getElementById('myModal');
// Get the main container and the body
var body = document.getElementsByTagName('body');
var container = document.getElementById('myContainer');
// Get the open button
var btnOpen = document.getElementById("myBtn");
// Get the close button
var btnClose = document.getElementById("closeModal");
// Open the modal
btnOpen.onclick = function() {
    modal.className = "Modal is-visuallyHidden";
    setTimeout(function() {
      container.className = "MainContainer is-blurred";
      modal.className = "Modal";
    }, 100);
    container.parentElement.className = "ModalOpen";
}
// Close the modal
btnClose.onclick = function() {
    modal.className = "Modal is-hidden is-visuallyHidden";
    body.className = "";
    container.className = "MainContainer";
    container.parentElement.className = "";
}
// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
    if (event.target == modal) {
        modal.className = "Modal is-hidden";
        body.className = "";
        container.className = "MainContainer";
        container.parentElement.className = "";
    }
}