Change modal script so it loads on page load instead of button click - modal-dialog

Question

I have the following code that I load through Google Tag Manager, but the problem is that this demo loads a button at the bottom. I don't want that. Instead I want to load this on page load.
<style>/* 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 {
background-color: #fefefe;
margin: auto;
padding: 20px;
border: 1px solid #888;
width: 80%;
}
/* The Close Button */
.close {
color: #aaaaaa;
float: right;
font-size: 28px;
font-weight: bold;
}
.close:hover,
.close:focus {
color: #000;
text-decoration: none;
cursor: pointer;
}
</style>
<!-- Trigger/Open The Modal -->
<button id="myBtn">Open Modal</button>
<!-- The Modal -->
<div id="myModal" class="modal">
<!-- Modal content -->
<div class="modal-content">
<span class="close">×</span>
<p>Test message</p>
</div>
</div>
<script>
// Get the modal
var modal = document.getElementById('myModal');
// Get the button that opens the modal
var btn = document.getElementById("myBtn");
// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];
// When the user clicks the button, open the modal
btn.onclick = function() {
modal.style.display = "block";
}
// When the user clicks on <span> (x), close the modal
span.onclick = function() {
modal.style.display = "none";
}
// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
</script>
I think I have to replace:
<button id="myBtn">Open Modal</button>
with something like:
<script>window.onload = function </script>
Could someone help me out? What do I need to complete the above line of code?

Answer 1

This is really easy: You need to replace
btn.onclick = function() {
modal.style.display = "block";
}
with
document.addEventListener('DOMContentLoaded', function() {
modal.style.display = "block";
})
or with
window.onload = function () {
modal.style.display = "block";
}
The first code will load the modal on DOM Ready and the second code will load the page on Window load.