How to reuse HTML across entire site
Solution 1:
The simplest way I believe is to use jQuery.
See jQuery docs here
one.html:
<html>
<head>
<script src="jquery.js"></script>
<script>
$(function(){
$("#header").load("two.html");
});
</script>
</head>
<body>
<div id="header"></div>
</body>
</html>
two.html:
<p> Put your header in here </p>
Solution 2:
If you don't want to store jquery, you can use a CDN
<html>
<head>
<script src="https://code.jquery.com/jquery-3.4.1.js"></script>
<script>$(document).ready(function () { $("header").load("assets/header.html"); });</script>
</head>
<body>
<header></header>
</body>
</html>