javascript联动菜单的问题

Question

         function showSort(num)  
            {
            merchandiseSort=document.all["merchandiseSort"];  
            merchandiseSort.length=0;
            var arr=[sort1,sort2,sort3,sort4,sort5,sort6,sort7,sort8]  
                 for(i=0;i  <arr[num][i].length;i++)  
                 {   
                    var oOption=document.createElement("option"); 
                    
                    merchandiseSort.options.add(oOption);  
                    oOption.innerHTML=arr[num][i]  
                    oOption.value=num-1;                  
                 }  
            }