基于ajax后臺(tái)返回的數(shù)據(jù)為空前臺(tái)顯示出現(xiàn)undefined的解決方法

$(document).ready(function () { 
 $("#rankTable tbody").html("");

 var id = 1;

  $.ajax({ 
   url:"bookInfo/bookInfo_rank.action", 
   type:"POST", 
   data:{}, 
   dataType:"json", 
   success:function (data) { 
   
     $(data).each(function(i,item)
     {
     var index = id++;
     var bookId = item.bookId;
     var bookName = item.bookName;
     var author = item.author;
     //判斷是否為空出現(xiàn)undefined；
     var translator = (item.translator==undefined ?"":item.translator);
     var ISBN = item.ISBN;
     var press = item.press;
     var page = item.page;
     var bookCase = item.bookCase;
     var totalNum = item.totalNum;
     var stock = item.stock;
     var borrowNum = item.borrowNum;
     var typeName = item.typeName;
     var str = 'tr> ' + 'td>' + index + 
     '/td>' + 'td>' + bookId + 
     '/td>' + 'td>' +bookName + 
     '/td>' + 'td>' + author+
     '/td>' +'td>'+translator+
     '/td>' +'td>'+ISBN+
     '/td>' +'td>'+press+
     '/td>' +'td>'+page+
     '/td>' +'td>'+bookCase+
     '/td>' +'td>'+totalNum+
     '/td>' +'td>'+stock+
     '/td>' +'td>'+borrowNum+
     '/td>' +'td>'+typeName+
     '/td>/tr>';
     
     $("#rankTable tbody").append(str);
     str = "";
     
     })
     
   },
   error:function(XMLHttpRequest, textStatus, errorThrown){
   alert("系統(tǒng)異常，請(qǐng)稍后重試！");
   alert(XMLHttpRequest.status);
      alert(XMLHttpRequest.readyState);
      alert(textStatus);
   } 
  })
});