购物车的前台管理程序---只与服务器交互一次（二、javascript部分）

cart.js

请存为cart.js，并且和前部分HTML放在同一个目录中

//------------------------------------------------------------------------------
//
// file name :       cart.js
//

// description:      购物车前台用javascript 函数库
//
// function list :   On_Cancel(txtAmount , txtSum)---- 取消该项
//                   On_Update()                  ---- 更新数量
//                   On_Del()                     ---- 全部删除
//                   UpdateDate()                 ---- 更新表单显示
//                   Round()                      ---- 四舍五入取指定小数位数
//
// Aurthor:          LiuYunpeng
//
// Date:             2000/09/03
//
// History:          2000/09/03 version 1.0
//
//------------------------------------------------------------------------------

//----------------code begin here------------------------------------------

  function On_Cancel(txtAmount , txtSum)
    {
      txtAmount.value = 0 ;
      txtSum.value = 0 ;
      UpdateData();     
    }

  //更新表单显示
  function UpdateData()
    {
      var m_aAmount   = new Array() ;
      var m_aPrice    = new Array() ;
      var m_aDiscount = new Array() ;
      var m_aSum      = new Array() ;
      var m_numTotal  = 0 ;
      var i , j , k  , m;
      i = 0 ;
      j = 0 ;
      k = 0 ;
      m = 0 ;
     
      //求数量
      for (i = 0 ; i < document.frmOrder .elements .length ; i ++ )
        {
           if (frmOrder.elements [i].name.substring(0 , 9) == "txtAmount")
             {
               m_aAmount[j] = frmOrder.elements [i].value ;
               j ++ ;
             }
           if (frmOrder.elements [i].name.substring(0 , 14) == "txtTicketPrice")
             {
             
              m_aPrice[k] = Round(frmOrder.elements[i].value , 2) ;
              k ++ ;
             }
           if (frmOrder.elements [i].name.substring(0 , 14) == "hidTicketDisco")
             {
              m_aDiscount[m] = frmOrder.elements[i].value ;
              m ++ ;
             }
         }
        
      for ( i = 0 ; i < k ; i ++)
         {
           m_aSum[i] = Round(m_aPrice[i] * m_aAmount[i] * m_aDiscount[i] / 100 , 2);
          
         }
                
                 
      //更新form
      j = 0 ;
      for (i = 0 ; i < document.frmOrder .elements .length ; i ++ )
        {
           if (frmOrder.elements [i].name.substring(0 , 6) == "txtSum")
             {
               frmOrder.elements [i].value = m_aSum[j] ;
               m_numTotal = Round(m_numTotal + m_aSum[j] , 2);
               j ++ ;
             }
            
         }
      
      document.frmOrder .txtTotal .value = m_numTotal ;
        
      return 0;             
   }      

  //更新数量
  function On_Update()
    {
   
      if (document.frmOrder .btnUpdate .value == "修改数量")
         {
          document.frmOrder .btnUpdate .value = "更新数量"
          for (var i=0 ; i < frmOrder.elements.length ; i++)
             {
               if (frmOrder.elements