这个条件中的值如何理解

function startMove(obj,att,add)
{
    clearInterval(obj.timer)
    obj.timer = setInterval(function(){
       var cutt = 0 ;
       if(att=='opacity')
       {
           cutt = Math.round(parseFloat(getStyle(obj,att)));
       }
       else
       {
           cutt = Math.round(parseInt(getStyle(obj,att)));
       }
       var speed = (add-cutt)/4;
       speed = speed>0?Math.ceil(speed):Math.floor(speed);
       if(cutt==add)
       {
           clearInterval(obj.timer)
       }
       else
       {
           if(att=='opacity')
           {
               obj.style.opacity = (cutt+speed)/100;
               obj.style.filter = 'alpha(opacity:'+(cutt+speed)+')';
           }
           else
           {
               obj.style[att] = cutt+speed+'px';
           }
       }
        
    },30)
}


    上面是一个js幻灯片的函数，其中

if(att=='opacity')
  {
  cutt = Math.round(parseFloat(getStyle(obj,att)));
  }
  else
  {
  cutt = Math.round(parseInt(getStyle(obj,att)));
  }
这两个条件中的cutt都代表什么