window.open问题求教

<script>
function openWin(url,width,height){
var phxWin=window.open(url,'null','width='+width+',height='+height+',left='+(screen.width-width)/2+',top='+(screen.height-height)/2+'');
phxWin.resizeTo(width,height)
phxWin.moveTo((screen.width-width)/2,+(screen.height-height)/2)
phxWin.focus();
}
</script>
<a onClick="openWin('QS.jsp',400,300)" style="cursor:hand" >签收</a>
<a onClick="openWin('abc.jsp',500,600)" style="cursor:hand" >再签收一次</a>

点击”签收”弹出一个窗口，当点击"再签收一次"时改变先前弹出的窗口宽、高分别为500,600.窗口里显示abs.jsp页面，效果如同上面给的代码一样。