请问这个左右键切换样式怎么写

function startMove(obj, json, fn)
{
clearInterval(obj.timer);
obj.timer=setInterval(function (){
var bStop=true; //这一次运动就结束了——所有的值都到达了
for(var attr in json)
{
//1.取当前的值
var iCur=0;

        if(attr=='opacity')
        {
            iCur=parseInt(parseFloat(getStyle(obj, attr))*100);
        }
        else
        {
            iCur=parseInt(getStyle(obj, attr));
        }

        //2.算速度
        var iSpeed=(json[attr]-iCur)/8;
        iSpeed=iSpeed>0?Math.ceil(iSpeed):Math.floor(iSpeed);

        //3.检测停止
        if(iCur!=json[attr])
        {
            bStop=false;
        }

        if(attr=='opacity')
        {
            obj.style.filter='alpha(opacity:'+(iCur+iSpeed)+')';
            obj.style.opacity=(iCur+iSpeed)/100;
        }
        else
        {
            obj.style[attr]=iCur+iSpeed+'px';
        }
    }

    if(bStop)
    {
        clearInterval(obj.timer);

        if(fn)
        {
            fn();
        }
    }
}, 30)

}

//以获取左右键对象
//上面的左右按钮
oBtnPrev.onmouseover=oMarkLeft.onmouseover=function ()
{
startMove(oBtnPrev, 'opacity', 100);
}

oBtnPrev.onmouseout=oMarkLeft.onmouseout=function ()
{
    startMove(oBtnPrev, 'opacity', 0);
}

oBtnNext.onmouseover=oMarkRight.onmouseover=function ()
{
    startMove(oBtnNext, 'opacity', 100);
}

oBtnNext.onmouseout=oMarkRight.onmouseout=function ()
{
    startMove(oBtnNext, 'opacity', 0);
}