Creating Multiple Modals on a Single Page

• You assigned the same Id to both modal triggering buttons. Different elements shouldn’t have the same Id.
• In you JavaScript code, you always pick a single element (a single close button, a single open button, etc).

It’s a HTML/JS beginner’s mistake I would say. This would work:

// Get the button that opens the modal
var btn = document.querySelectorAll("button.modal-button");

// All page modals
var modals = document.querySelectorAll('.modal');

// Get the <span> element that closes the modal
var spans = document.getElementsByClassName("close");

// When the user clicks the button, open the modal
for (var i = 0; i < btn.length; i++) {
 btn[i].onclick = function(e) {
    e.preventDefault();
    modal = document.querySelector(e.target.getAttribute("href"));
    modal.style.display = "block";
 }
}

// When the user clicks on <span> (x), close the modal
for (var i = 0; i < spans.length; i++) {
 spans[i].onclick = function() {
    for (var index in modals) {
      if (typeof modals[index].style !== 'undefined') modals[index].style.display = "none";    
    }
 }
}

// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
    if (event.target.classList.contains('modal')) {
     for (var index in modals) {
      if (typeof modals[index].style !== 'undefined') modals[index].style.display = "none";    
     }
    }
}

/* The Modal (background) */
.modal {
    display: none; /* Hidden by default */
    position: fixed; /* Stay in place */
    z-index: 1; /* Sit on top */
    padding-top: 100px; /* Location of the box */
    left: 0;
    top: 0;
    width: 100%; /* Full width */
    height: 100%; /* Full height */
    overflow: auto; /* Enable scroll if needed */
    background-color: rgb(0,0,0); /* Fallback color */
    background-color: rgba(0,0,0,0.4); /* Black w/ opacity */
}

/* Modal Content */
.modal-content {
    position: relative;
    background-color: #fefefe;
    margin: auto;
    padding: 0;
    border: 1px solid #888;
    width: 80%;
    box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2),0 6px 20px 0 rgba(0,0,0,0.19);
    -webkit-animation-name: animatetop;
    -webkit-animation-duration: 0.4s;
    animation-name: animatetop;
    animation-duration: 0.4s
}

/* Add Animation */
@-webkit-keyframes animatetop {
    from {top:-300px; opacity:0}
    to {top:0; opacity:1}
}

@keyframes animatetop {
    from {top:-300px; opacity:0}
    to {top:0; opacity:1}
}

/* The Close Button */
.close {
    color: white;
    float: right;
    font-size: 28px;
    font-weight: bold;
}

.close:hover,
.close:focus {
    color: #000;
    text-decoration: none;
    cursor: pointer;
}

.modal-header {
    padding: 2px 16px;
    background-color: #5cb85c;
    color: white;
}

.modal-body {padding: 2px 16px;}

.modal-footer {
    padding: 2px 16px;
    background-color: #5cb85c;
    color: white;
}

<h2>1st Modal</h2>

<!-- Trigger/Open The Modal -->
<button class="modal-button" href="#myModal1">Open Modal</button>

<!-- The Modal -->
<div id="myModal1" class="modal">

  <!-- Modal content -->
  <div class="modal-content">
    <div class="modal-header">
      <span class="close">×</span>
      <h2>Modal Header</h2>
    </div>
    <div class="modal-body">
      <p>Some text in the Modal Body</p>
      <p>Some other text...</p>
    </div>
    <div class="modal-footer">
      <h3>Modal Footer</h3>
    </div>
  </div>

</div>

<h2>2nd Modal</h2>

<!-- Trigger/Open The Modal -->
<button class="modal-button" href="#myModal2">Open Modal</button>

<!-- The Modal -->
<div id="myModal2" class="modal">

  <!-- Modal content -->
  <div class="modal-content">
    <div class="modal-header">
      <span class="close">×</span>
      <h2>Modal Header</h2>
    </div>
    <div class="modal-body">
      <p>Some text in the Modal Body</p>
      <p>Some other text...</p>
    </div>
    <div class="modal-footer">
      <h3>Modal Footer</h3>
    </div>
  </div>

</div>