I read when a writer shows me that she's got interesting stuff to say and isn't going to repeat what she's said previously. I scan when someone shows me what they're saying isn't important (a tl;dnr summary is a strong sign of something not being important) or can be easily summarized.
When I write, I write for people who realize what I'm writing can't be summarized to tl'dnr. That means I probably collect far fewer "hits," but I would tend to imagine those who do follow my work are more engaged.
And the scrolling js thing might tell even more than if they "scrolled to the bottom of the page", if it incorporated time data, i.e how much time it took them for each scrolling. If it took them long enough to scroll, then we can bet they actually read it.
When I write, I write for people who realize what I'm writing can't be summarized to tl'dnr. That means I probably collect far fewer "hits," but I would tend to imagine those who do follow my work are more engaged.