将iFrame中的鼠标位置中继到父窗口

Question

我有一个页面 A.html 我嵌入了 B.html ，我想在A.html中获得鼠标位置，有一个问题，当我的鼠标在 iframe 元素上点击A.html时，它不会显示鼠标位置

A.html

<style>
  .iframe_1{height:150px; width: 150px; top:360px; left:365px; overflow:hidden;
            position:absolute;}
</style>
<iframe id="iframe" class="iframe_1" src="http://www.example.com/B.html">
</iframe>

my.js

document.onclick=getMouPo;
function getMouPo(ev){
  if ( ev == null )
    ev = window.event;

  var point = {
    x:0,y:0
  };
  if ( typeof window.pageYOffset != 'undefined'){
    point.x = window.pageXOffset;
    point.y = window.pageYOffset;
  }
  else if(typeof document.compatMode != 'undefined' && document.compatMode != 'BackCompat'){
    point.x = document.documentElement.scrollLeft;
    point.y = document.documentElement.scrollTop;
  }
  else if(typeof document.body != 'undefined'){
    point.x = document.body.scrollLeft;
    point.y = document.body.scrollTop;
  }

  point.x += ev.clientX;
  point.y += ev.clientY;
  alert (point.x +","+ point.y);
  return point;
} // getMouPo(ev)