Add class when block is in scope?

Question

JavaScript

Is there something like a vertical timeline

Example

Example https://codepen.io/brezze/pen/VwvLBvY

When scrolling for a menu element, add an active class that corresponds to the block, and remove it from the previous one. How it is better to implement it?

I understand that you need to check when the content part is in the viewport, then add a class for the corresponding menu item, I just don’t fully understand how to implement it yet.