roop.js

function roop (c, a) {
	function cycle (t) {
    c() && a(t)
		return requestAnimationFrame(cycle)  
  }
  
  return cycle(performance.now())
}

let y = window.pageYOffset

roop(() => {
	const change = window.pageYOffset !== y
  y = window.pageYOffset
  return change
}, () => {
	console.log('is scrolling')
})