Calculate the distance of a give HTML element to viewport

get-distance-to-viewport.js

// could be replaced by getBoundingClientRect()
function getDistanceToViewport(element: HTMLElement) {
  let left = 0, top = 0, current: HTMLElement

  current = element
  while (current) {
    left += current.offsetLeft
    top += current.offsetTop
    current = current.offsetParent as HTMLElement
  }

  let scrollLeft = 0, scrollTop = 0;

  current = element
  while (current) {
    scrollLeft += current.scrollLeft
    scrollTop += current.scrollTop
    current = current.parentElement
  }

  left -= scrollLeft
  top -= scrollTop

  return { left, top }
}