Scroll progresively to the bottom of page javascript

scrollProgr.js

/**
* scrollProgr.js
* Scroll progresively to the bottom of a page.
*
* param: jump Number: Pixels to jump in each scroll
* param: time Number: ms between each scroll
* param: maxDistance Number: Don't do more jumps after surpassing this number
* param: timeou Number: Kill the scrolling after this number of ms
*
* return <promise> undefined | String
*/
function scrollProgr(jump, time, maxDistance=Infinity, timeout=null) {
  return new Promise((resolve,reject) => {
    let scrolledDistance = 0;
    if (timeout) {
      setTimeout(()=> {
        resolve(`Scroll timed out after ${timeout}ms`)
        clearInterval(scroll)
      }, timeout)
    }
    return scroll = window.setInterval(() => {
      let prevY = window.scrollY
      window.scrollTo(0, window.scrollY + jump)
      scrolledDistance += jump
      let newY = window.scrollY
      if (scrolledDistance >= maxDistance || prevY === newY) {
        clearInterval(scroll)
        console.log('Finished scrolling')
        resolve()
      }
    }, time)
  })
}