这处的if判断不大懂，speed正负和新left和原left值比较这一大串不就相当于偏移量存在嘛

function go(){   //变化图片动画效果
    if ((speed<0&&parseInt(list.style.left)>newLeft)
    ||speed>0&&parseInt(list.style.left)<newLeft) {
    list.style.left = parseInt(list.style.left)+speed+"px";
    setTimeout(go,interval);  //在位移时就给予动画效果
    }else {
        change = false;   //切换完毕后可继续切换
        list.style.left = newLeft + "px";
        if (newLeft > -600) {                                
        list.style.left = -3000 + "px";                            
        }                            
        if (newLeft < -3600) {                                
        list.style.left = -1200 + "px";                            
        }                        
    }                    
}