Can u plz help me to open a model window with button click in javascript?

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

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

  <!-- Modal content -->
  <div class="modal-content">
    <span class="close">×</span>
    <p>Some text in the Modal..</p>
  </div>

</div>
<pre>

*****js******:
<pre>r modal = document.getElementById('myModal');

var btn = document.getElementById("myBtn");

var span = document.getElementsByClassName("close")[0];
 
btn.onclick = function() {// here I get error 
    modal.style.display = "block";
}
span.onclick = function() {
    modal.style.display = "none";
}


window.onclick = function(event) {
    if (event.target == modal) {
        modal.style.display = "none";
    }
}