JavaScript获取鼠标相对于浏览器窗口坐标的方法

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title></title>
<style type="text/css">
#test_div {
  width:400px;
  height: 400px;
  background-color: red;
}
</style>
  </head>
  <body>
  <div id="test_div"></div>
  </body>
<script type="text/javascript">
  function mousePos(e){
    e=e||window.event;
    var scrollX=document.documentElement.scrollLeft||document.body.scrollLeft;//分别兼容ie和chrome
    var scrollY=document.documentElement.scrollTop||document.body.scrollTop;
    var x=e.pageX||(e.clientX+scrollX);//兼容火狐和其他浏览器
    var y=e.pageY||(e.clientY+scrollY);
    console.log(x,y);
    return {x:x,y:y};
  }
  var test=document.querySelector("#test_div");
  test.onclick=function(e){
    mousePos(e);
  }
</script>
</html>