https://www.skydiv.jp/thin_client/article/js/submenu.js

1const makeSubnavi = function(){
2	document.addEventListener('DOMContentLoaded', function() {
3		title = document.querySelectorAll('.contents__title');
4		if(title.length > 0){
5			let i = 1;
6			let listWraper = document.querySelector('#js-anchor');
7
8			title.forEach(items => {
9				let text = items.textContent;
10				let id = `p${i}`;
11				if(items.hasAttribute('id')) {
12					id = items.getAttribute('id');
13				}else{
14					items.setAttribute('id',id);
15				}
16				const listItem = document.createElement('li');
17				listItem.innerHTML = `<a href="#${id}">${text}</a>`;
18				listWraper.appendChild(listItem);
19				i = i + 1;
20			})
21		}
22	})
23}