Get a list of moves available to a specific player using boardgame.io

getAvailableMoves.js

/**
 * Get a list of the moves that are currently available to a specific player.
 *
 * @param {import("boardgame.io").Game} game boardgame.io game object
 * @param {import("boardgame.io").Ctx} ctx current game context object
 * @param {import("boardgame.io").PlayerID} playerID the ID of the player to get moves for
 * @returns {string[]} an array of move names
 *
 * @example
 * const game = {
 *   moves: { A: () => {} },
 * };
 * const ctx = { currentPlayer: '0', phase: null, activePlayers: null };
 *
 * getAvailableMoves(game, ctx, '0'); // ['A']
 * getAvailableMoves(game, ctx, '1'); // []
 */
function getAvailableMoves(game, ctx, playerID) {
  const { phase, activePlayers, currentPlayer } = ctx;
  const stage = activePlayers ? activePlayers[playerID] : undefined;
  // If some players are in stages, but not this one, they can’t make a move.
  if (activePlayers && stage === undefined) return [];
  // If no players are in stages, only the current player can make a move.
  if (!activePlayers && playerID !== currentPlayer) return [];

  let phaseConfig = game;
  if (phase) phaseConfig = game.phases[phase];
  const { moves } = stage ? phaseConfig.turn.stages[stage] : phaseConfig;
  return Object.keys(moves);
}