Function observePosition

src/index.ts:145–177

* Observe this elements position. * @param el - The element to observe the position of.

(el: Element)

 * @param el - The element to observe the position of.
 */
function observePosition(el: Element) {
  const oldObserver = intersections.get(el)
  oldObserver?.disconnect()
  let rect = coords.get(el)
  let invocations = 0
  const buffer = 5
  if (!rect) {
    rect = getCoords(el)
    coords.set(el, rect)
  }
  const { offsetWidth, offsetHeight } = root
  const rootMargins = [
    rect.top - buffer,
    offsetWidth - (rect.left + buffer + rect.width),
    offsetHeight - (rect.top + buffer + rect.height),
    rect.left - buffer,
  ]
  const rootMargin = rootMargins
    .map((px) => `${-1 * Math.floor(px)}px`)
    .join(" ")
  const observer = new IntersectionObserver(
    () => {
      ++invocations > 1 && updatePos(el)
    },
    {
      root,
      threshold: 1,
      rootMargin,
    },
  )
  observer.observe(el)
  intersections.set(el, observer)
}

/**
 * Update the exact position of a given element.