Update URL hash based on heading in view

[chrissy-dev]

This is something I noticed while reading through the README on the website — the URL didn’t update as I scrolled, so using the back button wouldn’t take me to the last section I was reading.

This PR adds a small script that watches which heading is visible on screen and updates the #anchor in the browser's URL. That way, you can scroll around, and the browser history reflects where you are.

What changed

• Uses IntersectionObserver to detect which heading is currently in view
• Updates the URL hash (#heading-name) without reloading the page
• Works with the heading IDs created by marked-gfm-heading-id, even when they start with - (which is fine in modern browsers)

Let me know if this feels too extra — just thought it was a nice little UX improvement.

[offa]

This sounds like a good idea! I just have to figure out how to actually try it 😅.

[offa]

Looks like the only easy way to try it is testing it locally 🤔.

Now, I'm not sure if I understand this feature correctly. Let's say i click on Calendar in the ToC, jump to it's section and the url is updated. Where should the back button bring me?

In my case I got back to Toc, but with some section in the url I didn't visit.

[chrissy-dev]

Hey! Just wanted to say thanks for taking the time to look at this.

I’m going to go ahead and close the PR — turns out this was a bit of a false alarm. I recently moved over to Android from iOS and was going through the (super helpful) list on the site. At the time, I noticed that using the back/forward buttons didn’t take me to the section I was previously reading, so I thought updating the anchors on scroll would help.

But I’ve just gone back to do a quick comparison video… and now everything’s working exactly as I’d expect 😅 God knows what was going on the first time — maybe a glitch or browser quirk on my end.

Apologies for the noise, and thanks again!

[offa]

No problem, still thank you for your contribution! 😃