笨笨JS问题。怎么通过JS来更换一个项的样式.怎么换?

<!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>测试页面</title>
<style type="text/css">
span{color:#FF0000;}
.myspan{color:#FF0000;}
.changespan{color:#0000FF;}
</style></head>
<body>
<div id="marqueedivcontrol" style="width:100px;height:200px;overflow:hidden; background-color:#dddddd;">
<span id="S1" name="ListItem">aaaaaaaaaa</span><br />
<span id="S2" name="ListItem">bbbbbbbbbb</span><br />
<span id="S3" name="ListItem">cccccccccc</span><br />
<span id="S4" name="ListItem">dddddddddd</span><br />
<span id="S5" name="ListItem">eeeeeeeeee</span><br />
<span id="S6" name="ListItem">ffffffffff</span><br />
<span id="S7" name="ListItem">gggggggggg</span><br />
<span id="S8" name="ListItem">hhhhhhhhhh</span><br />
</div>
<input type="button" value="向上" id="top1" onclick="top1onclick()" />
<input type="button" value="向下" id="bottom1" onclick="bottom1onclick" /><script type="text/javascript">
var i=0;
var DivArray = new Array();
DivArray = document.getElementById("marqueedivcontrol").childNodes;
var DivLength=DivArray.lenght;function top1onclick()
{DivArray[i].className="myspan";
changei(true);
alert(i);
DivArray[i].className="changespan";
}
function bottom1onclick()
{
DivArray[i].className=myspan;
changei(flase);
alert(i);
DivArray[i].className=changespan;
}function changei(mybool)
{
if (mybool)
{
if(i<(DivLength-1))
{
i++;
}
else
{
i=0;//大于索引时，回到0；
}
}
else
{
if(i=0)
{
i=DivLength-1;//等于零时，回到最大值；
}
else
{
i--;
}
}
}
</script>
</body>
</html>

解决方案 »

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刚刚开始写js是不是，有很多不应该的错误在里面，下面的是调试好的，你对着你自己的好好的对一下问题主要下面几个方面：
1，文档加载之前就去掉用控件了
2，比较运算应该是==，你写成=了
3，DivArray本身就是个控件数组，你又去掉用getElementById了
4，更改样式应该是className而不是class
5，给样式赋值应该给css加上引号
<!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>测试页</title>
<style type="text/css">
    span{color:#FF0000;}
    .myspan{color:#FF0000;}
    .changespan{color:#0000FF;}
</style>
</head>
<body>
    <div id="marqueedivcontrol" style="width:100px;height:200px;overflow:hidden; background-color:#dddddd;">
        <span id="S1" name="ListItem">aaaaaaaaaa</span><br />
        <span id="S2" name="ListItem">bbbbbbbbbb</span><br />
        <span id="S3" name="ListItem">cccccccccc</span><br />
        <span id="S4" name="ListItem">dddddddddd</span><br />
        <span id="S5" name="ListItem">eeeeeeeeee</span><br />
        <span id="S6" name="ListItem">ffffffffff</span><br />
        <span id="S7" name="ListItem">gggggggggg</span><br />
        <span id="S8" name="ListItem">hhhhhhhhhh</span><br />
    </div>
    <input type="button" value="向上" id="top1" onclick="top1onclick()" />
    <input type="button" value="向下" id="bottom1" onclick="bottom1onclick()" />
</body>
<script type="text/javascript">
        var i=0;
        var DivArray = document.getElementById("marqueedivcontrol").getElementsByTagName("span");
        var DivLength=DivArray.length;       function top1onclick()
        {
            DivArray[i].className="myspan";
            changei(false);
            DivArray[i].className="changespan";
        }
        function bottom1onclick()
        {
            DivArray[i].className="myspan";
            changei(true);
            DivArray[i].className="changespan";
        }        function changei(mybool)
        {
            if (mybool)
            {
                if(i<(DivLength-1))
                {
                    i++;
                }
                else
                {
                    i=0;//大于索?时，回到0；
                }
            }
            else
            {
                if(i==0)
                {
                    i=DivLength-1;//等于零时，回到畜值；
                }
                else
                {
                    i--;
                }
            }
        }
    </script></html>
<!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>测试页面</title>
<style type="text/css">
span{color:#FF0000;}
.myspan{color:#FF0000;}
.changespan{color:#0000FF;}
</style>
<script type="text/javascript">
var i=0;
DivArray = document.getElementsByTagName("span");
var DivLength=DivArray.length;

   function top1onclick()
{
for (var i=0;i<DivArray.length;i++)
{
DivArray[i].className="myspan";
changei(true);
alert(i);
DivArray[i].className="changespan";
}
}
function bottom1onclick()
{
for (var i=0;i<DivArray.length;i++)
{
DivArray[i].className="myspan";
changei(false);
alert(i);
DivArray[i].className="changespan";
}
}

function changei(mybool)
{
if (mybool)
{
if(i<(DivLength-1))
{
i++;
}
else
{
i=0;//大于索引时，回到0；
}
}
else
{
if(i=0)
{
i=DivLength-1;//等于零时，回到最大值；
}
else
{
i--;
}
}
}
</script>
</head>
<body>
<div id="marqueedivcontrol" style="width:100px;height:200px;overflow:hidden; background-color:#dddddd;">
<span id="S1" name="ListItem">aaaaaaaaaa</span><br />
<span id="S2" name="ListItem">bbbbbbbbbb</span><br />
<span id="S3" name="ListItem">cccccccccc</span><br />
<span id="S4" name="ListItem">dddddddddd</span><br />
<span id="S5" name="ListItem">eeeeeeeeee</span><br />
<span id="S6" name="ListItem">ffffffffff</span><br />
<span id="S7" name="ListItem">gggggggggg</span><br />
<span id="S8" name="ListItem">hhhhhhhhhh</span><br />
</div>
<input type="button" value="向上" id="top1" onclick="top1onclick()" />
<input type="button" value="向下" id="bottom1" onclick="bottom1onclick()" />
</body>
</html>
你错误太多了....无语!