                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /焦点图轮播特效

老师提供的源代码里，这一段是什么意思？视频里面好像没有讲？

var go = function (){
                    if ( (speed > 0 && parseInt(list.style.left) < left) || (speed < 0 && parseInt(list.style.left) > left)) {
                        list.style.left = parseInt(list.style.left) + speed + 'px';
                        setTimeout(go, inteval);
                    }
                    else {
                        list.style.left = left + 'px';
                        if(left>-200){
                            list.style.left = -600 * len + 'px';
                        }
                        if(left<(-600 * len)) {
                            list.style.left = '-600px';
                        }
                        animated = false;
                    }
                }

中的

if(left>-200){
list.style.left = -600 * len + 'px';
}
if(left<(-600 * len)) {
list.style.left = '-600px';
}