function createOrUpdate(z, x, y, tileCoord) {
  if (tileCoord !== undefined) {
    tileCoord[0] = z;
    tileCoord[1] = x;
    tileCoord[2] = y;
    return tileCoord;
  }
  return [z, x, y];
}
@param {number} z Z.
@param {number} x X.
@param {number} y Y.
@param {TileCoord} [tileCoord] Tile coordinate.
@return {TileCoord} Tile coordinate.