判断鼠标是否移出事件

function isMouseOut(e, handler) {
  if (e.type !== "mouseout") {
    return false;
  }
  var reltg = e.relatedTarget
    ? e.relatedTarget
    : e.type === "mouseout"
    ? e.toElement
    : e.fromElement;
  while (reltg && reltg !== handler) {
    reltg = reltg.parentNode;
  }
  return reltg !== handler;
}