javascript弹出窗口居中

function selectCustomer(){
   var iTop = (window.screen.availHeight-30-500)/2;
   var iLeft = (window.screen.availWidth-10-750)/2;
   window.open("../customer/creditApprManage.do?method=toGetCustomer",
               "searchCorp",
               "height=500,width=750,top="+iTop+",left="+iLeft+",toolbar=no,menubar=no,scrollbars=auto,resizeable=no,location=no,status=no"
               );
  }

说明：500和750是硬编码，可以通过参数传入。