title: How can I trigger a function when a section touches the top of the viewport with Vanilla JS?
body: <p>I basically want the browser to trigger a function when a section touches the top of the viewport as the user scrolls and I'm not really sure how to do this with Vanilla JS. </p>
  
  <p>I've found some jQuery alternatives, but I'm just trying to figure out how Javascript works at the moment, so I'm not exactly sure where to begin or what to google for that matter. </p>