[JavaScript] Modal (Popup)

<!-- Button trigger modal -->
<button type="button" data-toggle="modal" data-target="#myModal">
  Launch demo modal
</button>

<!-- Modal -->
<div class="modal" id="myModal">
  <h4>Modal Title</h4>
  <p>
     Lorem ipsum dolor sit amet, consectetur adipiscing elit. Maecenas turpis
     felis, tempus sit amet sollicitudin quis, aliquet ut felis.
     Nam a malesuada sem.
  </p>
  <button type="button" data-dismiss="modal">Close</button>
</div>

.modal {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translateX(-50%) translateY(-50%);
  background: azure;
  padding: 1rem;
  border-radius: 1rem;
  border: 1px solid gray;
  display: none;
}

'use strict';

var launchBtns = document.querySelectorAll("button[data-toggle='modal']");
for (var i=0; i < launchBtns.length; i++) {
  var launchBtn = launchBtns[i];

  // when user click launch button, show modal.
  launchBtn.addEventListener("click", function(e) {
    var selector = e.target.dataset.target;
    var modal = document.querySelector(selector);
    modal.style.display = "block";

    if (modal.dataset.isSetClose != "true") {
      // when user click button with `data-dismiss="modal"` in the modal,
      // close the modal
      var closeBtns = modal.querySelectorAll("button[data-dismiss='modal']");
      for (var j=0; j < closeBtns.length; j++) {
        var closeBtn = closeBtns[j];
        closeBtn.addEventListener("click", function(e) {
          modal.style.display = "none";
        });
      }

      modal.dataset.isSetClose = "true";
    }
  });
}