Question

js 用firefox的firebug报错误 document.getElementById(cid) is null

firebug显示错误是document.getElementById(cid) is null
请问为什么
还包括了个<script src="js/prototype.js" type=text/javascript></script>
<script src="js/fabtabulous.js" type=text/javascript></script>

<script type=text/javascript>

var initialtab = [1, "sc1"]

var previoustab = "";
var intv;

function expandcontent(cid, aobject)
{
stopTimer();

highlighttab(aobject)

if (previoustab != "")
document.getElementById(previoustab).style.display = "none"

document.getElementById(cid).style.display = "block"//错误出现在这一行
previoustab = cid
}

function highlighttab(aobject)
{
stopTimer();

if (typeof tabobjlinks == "undefined")
collectddimagetabs()

for (i = 0; i < tabobjlinks.length; i++)
tabobjlinks[i].className = ""

aobject.className = "current"
}

function collectddimagetabs()
{
var tabobj = document.getElementById("ddimagetabs")
tabobjlinks = tabobj.getElementsByTagName("a")
}

function do_onload()
{
collectddimagetabs()
expandcontent(initialtab[1], tabobjlinks[initialtab[0] - 1])
}

function startTimer()
{
intv = setTimeout("expandcontent(initialtab[1], tabobjlinks[initialtab[0]-1])", 2000);
}

function stopTimer()
{
clearTimeout(intv);
}

Event.observe(window, 'load', do_onload, false);
Event.observe('xcx_tabmenu', 'mouseover', function(event)
{
stopTimer();
}, false);

Event.observe('xcx_tabmenu', 'mouseout', function(event)
{
var reltg = (event.relatedTarget) ? event.relatedTarget : event.toElement;

var tg = (window.event) ? event.srcElement : event.target;

if (tg.nodeName != 'div')
return;

while (reltg != tg && reltg.nodeName != 'body')
{
reltg = reltg.parentNode;

if (reltg.id == "xcx_tabmenu")
return;
}

if (reltg == tg)
return;

stopTimer();
startTimer();
}, false);
</script>

Answer 1

因为在当前document文档不存在一个id为形参cid的控件,所以浏览器无法应用该控件.

首先确定形参cid不为空,你在
function expandcontent(cid, aobject)
{
这个位置用
alert(cid);
测试一下cid是否有值,再判断cid是否在当前文档有对应的控件,id为cid的值.如果以上发现有问题.
下面你再用
document.getElementById(cid)...的时候就会出错.为了避免错误.可加一些判断.如
把你要执行的代码放在
if(document.getElementById(cid)){
//代码实现.
}

Answer 2

在这行前面加：if(!cid ||!document.getElementById(cid))return;