animation

example.js

const origin = window.pageYOffset
const destination = 3000

animate({
  duration : 500,
  tick(progress) {
    window.scrollTo(
      0,
      progress * destination +
      (1 - progress) * origin
    )
  }
})
  .then(() => console.log("done"))

lib.js

const duration = 300
const tick = () => {}

function animate({duration, tick} = {duration, tick}) {
  return new Promise((resolve) => {
    const start = Date.now()
    const onTick = () => {
      const now = Date.now()
      const progress = (now - start) / duration
      if(progress >= 1) {
        tick(1)
        resolve()
        return
      }
      tick(progress)
      requestAnimationFrame(onTick)
    }
    requestAnimationFrame(onTick)
  })
}