Inside the constructor of the Tile definition, we store a Boolean value to determine whether this tile is an obstacle. Since most of the tiles aren't obstacles, we initialize this variable with false:

this.isBlock = false;
for (var i = 0, len=game.BLOCKS.length; i < len; i++) {
  if (type === game.BLOCKS[i]) {
    this.isBlock = true;
  }
};

The following code inside the moveDown function of a tile, checks whether the tile collides with the player, when the tile itself is an obstacle:

if (this.isBlock) {
  this.checkCollison();
}

Next, we define the checkCollision function inside the Tile definition. It uses the position coordinates to determine...