帮忙看段js报错。。

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
</head>
<script src="js/jquery.js" type="text/javascript"></script>
<script src="js/dialog.js" type="text/javascript"></script>
<script src="js/common.js" type="text/javascript"></script>
<body>
<form id="askform" name="askform" method="post" action="">
<table border="0" cellpadding="0" cellspacing="0" width="50%">
  <tr valign="top">
    <td width="15%"><div class="tiwen2 tiw_kuai">
      <select  id="ClassLevel1" style="width: 125px; height: 165px;" size="8" name="classlevel1">
        <option selected="selected"></option>
      </select>
    </div></td>
    <td align="center" valign="middle" width="5%"><div><b>→</b></div></td>
    <td width="17%"><div class="tiwen2">
      <select  id="ClassLevel2"  style="width: 125px; height: 165px;" size="8" name="classlevel2">
        <option selected="selected"></option>
      </select>
    </div></td>
    <td align="center" valign="middle" width="6%"><div style="display: none;" id="jiantou"><b>→</b></div></td>
    <td width="1%"></td>
    <td width="19%"><select id="ClassLevel3"  style="width: 125px; height: 165px; display: none;" size="8" onchange="getCidValue();"  name="classlevel3">
      <option selected="selected"></option>
    </select>
    </td>
    <td width="32%"></td>
  </tr>
  <tr valign="top">
    <td class="tiw_biaozhu" colspan="5" align="left" valign="middle">请您选择正确的分类，以使您的问题尽快得到解答。</td>
  </tr>
</table></form>
<script type="text/javascript">
    var sortobj=eval('({"category1":[["1","妇科"],["2","产科"],["3","避孕流产"],["4","不孕不育"],["5","妇幼保健"],["6","乳腺疾病"]],"category2":[["3","24","药流"],["2","17","高危妊娠"],["1","30","卵巢囊肿"],["1","7","妇科炎症"],["2","18","产后出血"],["3","25","普通人流"],["1","8","月经不调"],["1","9","宫颈糜烂"],["2","19","产褥感染"],["3","26","无痛人流"],["2","20","宫外孕"],["1","10","阴道炎"],["3","27","避孕及安全期"],["3","28","引产"],["1","11","附件炎"],["2","21","妊高症"],["3","29","其他"],["2","22","早产"],["1","12","子宫肌瘤"],["2","23","其他"],["1","13","子宫内膜炎"],["1","14","盆腔炎"],["1","15","外阴白斑"],["1","16","其他"]],"category3":[]})');
    var g_ClassLevel1;
    var g_ClassLevel2;
    var g_ClassLevel3;
    var class_level_1=sortobj.category1;
    var class_level_2=sortobj.category2;
    var class_level_3=sortobj.category3;
    var button_noselect="不选择";    function getCidValue()
    {
        var _cl1 = document.askform.ClassLevel1;

        var _cl2 = document.askform.ClassLevel2;
        var _cl3 = document.askform.ClassLevel3;
        var _cid = document.askform.cid;
        if(_cl1.value!=0) _cid.value = _cl1.value;
        if(_cl2.value!=0) _cid.value = _cl2.value;
        if(_cl3.value!=0) _cid.value = _cl3.value;
    }
    function FillClassLevel1(ClassLevel1)
    {
        ClassLevel1.options[0] = new Option("aa", "0");
        for(i=0; i<class_level_1.length; i++)
        {
            ClassLevel1.options[i] = new Option(class_level_1[i][1], class_level_1[i][0]);
        }
        // ClassLevel1.options[0].selected = true;
        ClassLevel1.length = i;
    }
    function FillClassLevel2(ClassLevel2, class_level_1_id)
    {
        ClassLevel2.options[0] = new Option(button_noselect, "");
        count = 1;
        for(i=0; i<class_level_2.length; i++){
            if(class_level_2[i][0].toString() == class_level_1_id) {
                ClassLevel2.options[count] = new Option(class_level_2[i][2], class_level_2[i][1]);
                count = count+1;}
        }
        ClassLevel2.options[0].selected = true;
        ClassLevel2.length = count;
    }
    function FillClassLevel3(ClassLevel3, class_level_2_id)
    {
        ClassLevel3.options[0] = new Option(button_noselect, "");
        count = 1;
        for(i=0; i<class_level_3.length; i++) {
            if(class_level_3[i][0].toString() == class_level_2_id) {
                ClassLevel3.options[count] = new Option(class_level_3[i][2], class_level_3[i][1]);
                count = count+1;}
        }
        ClassLevel3.options[0].selected = true;
        ClassLevel3.length = count;
    }
    function ClassLevel2_onchange()
    {
        getCidValue();
        FillClassLevel3(g_ClassLevel3, g_ClassLevel2.value);
        if (g_ClassLevel3.length <= 1) {
            g_ClassLevel3.style.display = "none";
            document.getElementById("jiantou").style.display = "none";
        }
        else {
            g_ClassLevel3.style.display = "";
            document.getElementById("jiantou").style.display = "";
        }
    }
 
    function ClassLevel1_onchange()
    {
        getCidValue();
        FillClassLevel2(g_ClassLevel2, g_ClassLevel1.value);
        ClassLevel2_onchange();    }
    function InitClassLevelList(ClassLevel1, ClassLevel2, ClassLevel3)
    {
        g_ClassLevel1=ClassLevel1;
        g_ClassLevel2=ClassLevel2;
        g_ClassLevel3=ClassLevel3;
        g_ClassLevel1.onchange = Function("ClassLevel1_onchange();");
        g_ClassLevel2.onchange = Function("ClassLevel2_onchange();");
        FillClassLevel1(g_ClassLevel1);
        ClassLevel1_onchange();
    }
    InitClassLevelList(document.askform.ClassLevel1, document.askform.ClassLevel2, document.askform.ClassLevel3);    var selected_id_list="0"
    var blank_pos = selected_id_list.indexOf(" ");
    var find_blank = true;
    if (blank_pos == -1) {
        find_blank = false;
        blank_pos = selected_id_list.length;
    }
    var id_str = selected_id_list.substr(0, blank_pos);
    g_ClassLevel1.value = id_str;
    ClassLevel1_onchange();    if (find_blank == true) {
        selected_id_list = selected_id_list.substr(blank_pos + 1,   selected_id_list.length - blank_pos - 1);
        blank_pos = selected_id_list.indexOf(" ");
        if (blank_pos == -1) {
            find_blank = false;
            blank_pos = selected_id_list.length;
        }
        id_str = selected_id_list.substr(0, blank_pos);
        g_ClassLevel2.value = id_str;
        ClassLevel2_onchange();        if (find_blank == true) {
            selected_id_list = selected_id_list.substr(blank_pos + 1,  selected_id_list.length - blank_pos - 1);
            blank_pos = selected_id_list.indexOf(" ");
            if (blank_pos == -1) {
                find_blank = false;
                blank_pos = selected_id_list.length;
            }
            id_str = selected_id_list.substr(0, blank_pos);
            g_ClassLevel3.value = id_str;
        }
    }    /*检查*/
    function check_askform(obj){
        if (bytes(obj.title.value) < 8 ||  bytes(obj.title.value)>60) {
            alert("问题标题长度不得少于4个字，不能超过30字！");
            obj.title.focus();
            return false;
        }
        /*
        if(obj.description.value ==""){
                alert("问题描述不能为空!");
                obj.description.focus();
                return false;
        }*/
        if(obj.classlevel1.selectedIndex==-1){
            alert("没有选择分类!");
            return false;
        }
            }
</script>
</body>
</html>