code: function(){
      this.frameIndex++;
      if (this.frameIndex >= this.rightCropPosition) {
        this.frameIndex = this.frameIndex % (this.rightCropPosition || 1);
  
        if ((this.frameIndex < this.leftCropPosition)) {
          this.frameIndex = this.leftCropPosition;
        }
      }else{
        this.frameIndex--;
      }
    }
docs: resets to beginning if at end