js计算表格的值(例如购物车中)

<script language="JavaScript" type="text/javascript" src="../js/jquery-1.7.min.js"></script>
 <script language="javascript" type="text/javascript"> 
 function   trim(str){return   str.replace(/^\s+|\s+$/,'')}
 function checkisempty(obj)
 {  
  var number=obj.value;
  var tr = obj.parentNode.parentNode;
  var tdpricevalue=$("#tbShopCar tr:eq(1) td:nth-child(7)").html();
  var tdnumbervalue=$('#tbShopCar td').find('input').val()
   //$("#table1 tr:eq(1) td:nth-child(1)").html("value");//设置table1,第2个tr的第一个td的值
  var qua=tdpricevalue*tdnumbervalue;
 $("#tbShopCar tr:eq(1) td:nth-child(8)").html(qua.toFixed(2));//相乘后结果保留两位小数
}
 </script>