A function to calculate possible coordinates for a knight on a chess board.

chessKnightMoves.ts

type Coordinate = [number, number];

/**
 * @desc gets all possible coordinates for a knight given its current position
 * @param x knight's current x position
 * @param y knight's current y position
 *
 * @example possibleDestinations(4, 3) => [[3, 1], [3, 5], [5, 5], [5, 1], [2, 2], [2, 4], [6, 2], [6, 4]]
 *
 * @returns all possible coordinates for the knight
 */
const possibleDestinations = (x: number, y: number): Coordinate[] => {
  if (!isValidCoordinate([x, y])) {
    throw new Error("Invalid chess board position");
  }

  return KNIGHT_POSSIBLE_L_MOVES.map<Coordinate>(([xMove, yMove]) => [
    xMove + x,
    yMove + y,
  ]).filter(isValidCoordinate);
};

const KNIGHT_POSSIBLE_L_MOVES: Coordinate[] = [
  [-1, -2],
  [-1, 2],
  [1, 2],
  [1, -2],
  [-2, -1],
  [-2, 1],
  [2, -1],
  [2, 1],
];

const isValidCoordinate = (coordinate: Coordinate) =>
  coordinate.every(isValidChessBoardPosition);

const CHESS_BOARD_LOWER_BOUND = 0;
const CHESS_BOARD_UPPER_BOUND = 7;

const isValidChessBoardPosition = (position: number) =>
  position >= CHESS_BOARD_LOWER_BOUND &&
  position <= CHESS_BOARD_UPPER_BOUND &&
  position % 1 === 0;