no detecta ID

[ClubIce]

Código Javascript:

Animation=function(spr,spd) {
 this.initialize({
  sprite:spr,
  speed:spd,
  frames:[],
  timer:null,
  count:0,
  id:null
 });
}
Animation.prototype={
 addFrame: function (id) {
  spr=this
  this.frames[frames.length]={
   id:id,
   sprite:"url('"+spr.sprite.image.src+"') "+spr.sprite.frames[id].x+"px "+spr.sprite.frames[id].y+"px;"
  }
 },
 drawAnimation:function (con, id) {
  image=document.createElement('img')
  image.setAttribute('src','sprites/empy.gif')
  image.setAttribute('style',"background:"+this.frames[0].sprite)
  image.setAttribute('class','animation')
  image.setAttribute('width',this.sprite.width)
  image.setAttribute('height',this.sprite.height)
  image.setAttribute('id',id)
  this.id=image
  con.appendChild(image)
  this.timer=setInterval(this.play,this.speed);
 },
 play:function() {
  if (this.count=this.frames.length) {
   this.count=0
  } else {
   this.count++
  }
  this.id.style.background=this.frames[this.count]
 }
}