封装变速函数

 function getStyle(element,attr){
        return window.getComputedStyle ? window.getComputedStyle(element,null)[attr]:element.currentStyle[attr];
    }
  function biansu(element,json,fn) {
       clearInterval(element.timeId)
       element.setInterval(function () {
           var flag=true
           for (var attr in json){
               var current=parseInt(getStyle(element,attr))
               var target=json[attr];
               var step=(target-current)/10;
               step=step>0?Math.ceil(step):Math.floor(step);
               current+=step;
               element.style[attr]=current+"px";
               if (current!=target){
                   flag=false;
               }
           }
           if (flag){
               clearInterval(element.timeId);

               if (fn){
                   fn();
               }
           }
       },20)
   }