帮看下这段 js 代码是干啥的

function offset(el) {
  let left = 0
  let top = 0

  while (el) {
    left -= el.offsetLeft
    top -= el.offsetTop
    el = el.offsetParent
  }

  return {
    left,
    top,
  }
}

+号求得是 el 到 body 元素的偏移距离

-号是啥玩意.....