Awesome
on-intersect 
Call back when an element intersects with another.
Usage
var onIntersect = require('on-intersect')
var html = require('bel')
var el = html`<h1>Yay, we're a heading!</h1>`
onIntersect(el, function () {
console.log('Woot, component is visible!')
})
document.body.appendChild(html`
<main>
<div style="height: 110vh"></div>
${el}
<div style="height: 110vh"></div>
</main>
`)
API
stopObserving = onViewport(element, [opts], [onEnter], [onExit])
Call onEnter when an element scrolls into view, and onExit when an element
scrolls out of view. opts can be any value passed into the
InterSectionObserver
constructor.
stopObserving()
Stop the observer.
Installation
$ npm install on-intersect