momentum.js is a lightweight jQuery plugin that generates a customizable progress bar which attaches to your app's fixed-position
nav element and measures how far down the page you are as you scroll.
Want to see a demo?
You're looking at it! Scroll down the page to see the progress bar in action.
By default, progress down the page is measured from the vertical center of the viewport. For this demo, we'll track scroll progress on the
<main id="main-content"> wrapper around the main content of this page.