Website HTML

 <!-- HEADER LOAD HERE -->
<div id="header"></div>
<script>
  fetch("header.html")
    .then(res => res.text())
    .then(data => {
      document.getElementById("header").innerHTML = data;
    });
</script>

<!-- FOOTER LOAD HERE -->
<div id="footer"></div>
<script>
fetch("footer.html")
.then(res => res.text())
.then(data => {
document.getElementById("footer").innerHTML = data;
});
</script>

<script src="main.js"></script>

<!-- FOOTER -->
<div id="footer"></div>

<!-- HEADER -->
<div id="header"></div>