How to make such a "progressbar" when scrolling?

Question

css

Hello, tell me how to make such an animation, as on this site -
www.nytimes.com/newsgraphics/2013/10/13/russia ?
It is this effect that is interesting, when progress was displayed on a separate field on the site (in the sidebar as a link, for example) when scrolling (vertically or horizontally). For example, as in readers - when you scroll through the pages, or as here - the movement of an object along the route when scrolling vertically. How does is called? SVG animation?

Answer 1

Animated Map Path for Interactive Storytelling

Answer 2

This is done with stroke-dasharray, stroke-dashoffset on svg path