获取元素在页面中相对视扣的位置

function getBoundingClientRect(element){
  var scrollTop = document.documentElement.scrollTop
  var scrollLeft = document.documentElement.scrollLeft
  if(element.getBoundingClientRect){
    if(typeof arguments.callee.offset != "number"){
      var temp = document.createElement("div")
      temp.style.cssText = "position:absolute;left:0;top:0"
      document.body.appendChild(temp)
      arguments.callee.offset = -temp.getBoundingClientRect().top - scrollTop
      document.body.removeChild(temp)
      temp = null
    }
    var rect = element.getBoundingClientRect()
    var offset = arguments.callee.offset
    return {
      left: rect.left + offset,
      right: rect.right + offset,
      top: rect.top + offset,
      bottom: rect.bottom + offset
    }
  } else {
    var actualLeft = getElementLeft(element)
    var actualTop = getElementTop(element)
    return {
      left: actualLeft - scrollLeft,
      right: actualLeft + element.offsetWidth - scrollLeft,
      top: actualTop - scrollTop,
      bottom: actualTop + element.offsetHeight - scrollTop
    }
  }
}