如何判断数组的下限？(在线等待)

Question

IE5.0提示'length'不是对象.帮忙在看看！

Answer 1

<script>
var labels=new Array("圆形盘","名片盘");
alert(labels[labels.length-1]);
</script>

Answer 2

怪事，试试
labels["length"]-1

Answer 3

试labels["length"]-1
出现错误：'length'为空或不是对象

Answer 4

单独调试通过，但放在以下代码中总是出错！
function MM_jumpMenu(selObj){ //v3.0
switch (selObj.options[selObj.selectedIndex].value) 
{ 
case 'CD-R':
window.list.location="product/disc/cdr/Eplatina1.asp";
var obj=document.getElementById("Layer1"); 
obj.style.visibility='visible';
var obj2=document.getElementById("Layer2"); 
obj2.style.visibility='hidden';
var labels=new Array("E-MARK白金片","E-MARK黑片","刻录佳","数据宝","快乐数码","大师","SONY(原装)","柯达(原装)");
var values=new Array("product/disc/cdr/Eplatina1.asp","product/disc/cdr/Eblack1.asp","product/disc/cdr/kelujia.asp","product/disc/cdr/shujubao.asp","product/disc/cdr/HappyData1.asp","product/disc/cdr/Master.asp","product/disc/cdr/SONY.asp","product/disc/cdr/koda.asp"); 
break; 
case 'CD-RW':
window.list.location="product/disc/cdrw/e.asp";
var obj=document.getElementById("Layer1"); 
var obj2=document.getElementById("Layer2"); 
obj.style.visibility='hidden';
obj2.style.visibility='hidden';
var labels=new Array("E-MARK");
var values=new Array("product/disc/cdrw/e.asp"); 
break; 
case 'DVD-R': 
window.list.location="product/disc/dvdr/e.asp";
var obj=document.getElementById("Layer1"); 
var obj2=document.getElementById("Layer2"); 
obj.style.visibility='hidden';
obj2.style.visibility='hidden';
var labels=new Array("E-MARK");
var values=new Array("product/disc/dvdr/e.asp"); 
break;
case '异型盘': 
window.list.location="product/disc/abnormity/index1.asp";
var obj=document.getElementById("Layer1"); 
var obj2=document.getElementById("Layer2"); 
obj.style.visibility='hidden';
obj2.style.visibility='hidden';
var labels=new Array("圆形盘","名片盘");
var values=new Array("product/disc/abnormity/index1.asp","product/disc/abnormity/index2.asp"); 
break;
case '无标盘': 
window.list.location="product/disc/no/index.asp";
var obj=document.getElementById("Layer1"); 
var obj2=document.getElementById("Layer2"); 
obj.style.visibility='hidden';
obj2.style.visibility='hidden';
var labels=new Array("无标盘");
var values=new Array("product/disc/no/index.asp"); 
break;
} 
document.all.usercity.options.length=0;
出错：'length'为空或不是对象
for(var i=0;i<labels.length;i++) 
{ 
document.all.usercity.add(document.createElement("OPTION")); 
document.all.usercity.options[i].text=labels[i]; 
document.all.usercity.options[i].value=values[i]; 
} 
// 选择第一个选项 
document.all.usercity.selectedIndex=0;
}

Answer 5

应该是document.all.usercity.options.length=0;出错了吧？

Answer 6

问题已解决！谢谢各位先！
低级错误,原因是多了空格！
IE5.0监测出空格
IE6.0监测不出空格
...
总之，参与者加分！！！（虽然只有20分!:)@）