Using jQuery 'load' function we can break our HTML files into smaller parts

includingHTML.html

<script src="./js/jquery-3.6.0.js"></script>

<script>
	$(function () {
		const includes = $('[data-include]')
		$.each(includes, function(){
			let file = 'includes/' + $(this).data('include') + '.html'
			$(this).load(file)
		})
	})
</script>

<div data-include="main"></div>
<div data-include="footer"></div>