document.elementFromPoint(x,y)方法可以获取到鼠标移动中当前光标所在的元素,他接受2个参数,鼠标的X坐标和Y坐标

document.onmousemove=function(event){
  var e=event?event:window.event;
  var x=e.clientX;
  var y=e.clientY;
  var obj=document.elementFromPoint(x,y);
  console.log(obj.nodeName);
}