这是一个js计时器的代码，目前只能向上滚动数字，我想改成向下滚动的应该怎么办呢，跪谢各位大神~
function DigitRoll(a){if(this.container=document.querySelector(a.container),this.width=a.width||2,!this.container)throw Error("no container");this.container.style.overflow="hidden",this.rollHeight=parseInt(getComputedStyle(this.container).height),this.rollHeight<1&&(this.container.style.height="20px",this.rollHeight=20),this.setWidth()}DigitRoll.prototype={roll:function(a){var c,d,b=this;for(this.number=parseInt(a)+"",this.number.length<this.width?this.number=new Array(this.width-this.number.length+1).join("0")+this.number:this.number.length>this.width&&(this.width=this.number.length,this.setWidth()),c=this.container.querySelectorAll(".num"),d=0;d<c.length;d++)!function(a){var i,d=c[a],e=parseInt(d.querySelector("div:last-child").innerHTML),f=parseInt(b.number[a]),g=0,h="";if(e!=f){if(f>e)for(g=f-e,i=e;f+1>i;i++)h+="<div>"+i+"</div>";else{for(g=10-e+f,i=e;10>i;i++)h+="<div>"+i+"</div>";for(i=0;f+1>i;i++)h+="<div>"+i+"</div>"}d.style.cssText+="-ms-transition-duration:0s;-ms-transform:translateY(0);-moz-transition-duration:0s;-moz-transform:translateY(0);-webkit-transition-duration:0s;-webkit-transform:translateY(0);-o-transition-duration:0s;-o-transform:translateY(0)",d.innerHTML=h,setTimeout(function(){d.style.cssText+="-ms-transition-duration:1s;-ms-transition-delay:"+a*0+"s;-ms-transform:translateY(-"+b.rollHeight*g+"px);-moz-transition-duration:1s;-moz-transition-delay:"+a*0+"s;-moz-transform:translateY(-"+b.rollHeight*g+"px);-webkit-transition-duration:1s;-webkit-transition-delay:"+a*0+"s;-webkit-transform:translateY(-"+b.rollHeight*g+"px);-o-transition-duration:1s;-o-transition-delay:"+a*0+"s;-o-transform:translateY(-"+b.rollHeight*g+"px)"},0)}}(d)},setWidth:function(a){var b,c;for(a=a||this.width,b="",c=0;a>c;c++)b+='<div class="num" style="float:left;height:100%;line-height:'+this.rollHeight+'px"><div>0</div></div>';this.container.innerHTML=b}};
