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Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

[Unreleased]

[2.0.2] - 2026-04-09

Changed

  • removed misleading keywords (fen, board-game)
  • added threefold-repetition and draw-detection keywords

[2.0.1] - 2026-04-09

Fixed

  • Corrected README to match 2.0.0 API: removed nonexistent Game.fromFen() and game.fen(), documented new Game(position) constructor, fixed undo() / redo() return types (void, not this), fixed Move.promotion signature, removed MoveInput from exports listing.
  • Updated AGENTS.md to reflect single runtime dependency (@echecs/position), removed nonexistent src/fen.ts, added missing test files, removed stale references to isAttacked / applyMoveToState, updated naming convention examples.
  • Changed package.json keyword from no-dependencies to minimal-dependencies.

[2.0.0] - 2026-04-09

Changed

  • BREAKING: upgraded to @echecs/position v3. Color values are now 'white'/'black' (was 'w'/'b'). PieceType values are now full words ('pawn', 'knight', 'bishop', 'rook', 'queen', 'king') instead of single letters.
  • BREAKING: CastlingRights shape is now { white: { king, queen }, black: { king, queen } } (was { wK, wQ, bK, bQ }).
  • BREAKING: PromotionPieceType uses full words ('queen', 'rook', 'bishop', 'knight') instead of single letters.
  • BREAKING: constructor now accepts an optional Position argument instead of always starting from the initial position. new Game() still defaults to the starting position; new Game(position) starts from any Position.
  • BREAKING: MoveInput type merged into Move with optional promotion. Game.move() now takes Move directly.
  • Rewrote move generation to use position.reach() for pseudo-legal targets and position.derive() + isCheck for legality filtering. Removed all 0x88 internal board manipulation.
  • @echecs/fen moved from runtime dependency to devDependency. FEN parsing/serialization is no longer part of the public API.

Added

  • Local Move and PromotionPieceType types (removed from @echecs/position v3).
  • Re-exported STARTING_POSITION, EnPassantSquare, and SideCastlingRights from @echecs/position.
  • Full game playthrough test (81-move Fischer-Spassky 1972 Game 6) via @echecs/san.
  • Zobrist hash consistency tests (move/undo cycles, transpositions).
  • Regression edge-case tests ported from chess.js.

Removed

  • BREAKING: Game.fromFen() static method — construct a Position and pass it to new Game(position) instead.
  • BREAKING: game.fen() method — use @echecs/fen directly with game.position().
  • BREAKING: isAttacked() method — removed from Game. Position v3 no longer exposes attack queries.

[1.2.2] - 2026-04-04

Added

  • TSDoc comments on all public methods and the Game class itself, with examples, @throws, and @remarks where applicable.
  • Exported MoveInput interface as a public type.

[1.2.1] - 2026-03-30

Added

  • Descriptive error messages for illegal moves in Game.move(). Messages now explain why a move is illegal: no piece on square, opponent's piece, game over, piece has no legal moves, piece cannot reach target, missing promotion, or promotion not allowed.
  • Explicit tests for castling rights revocation when a rook is captured on its starting square (a1, h1, a8, h8).

[1.2.0] - 2026-03-20

Added

  • game.position() getter returning the current Position from @echecs/position.

Changed

  • Internal state replaced with Position from @echecs/position. The Game class is now a thin stateful wrapper (undo/redo, legal move caching) over an immutable Position core.
  • FEN parsing and serialization delegated to @echecs/fen.
  • Types (Color, Piece, Move, Square, CastlingRights, PieceType, PromotionPieceType) are now re-exported from @echecs/position.
  • Attack tables (ATTACKS, RAYS, PIECE_MASKS) imported from @echecs/position/internal instead of built locally.
  • Threefold repetition detection uses Zobrist hashes instead of FEN strings.
  • @echecs/position and @echecs/fen are now runtime dependencies.

Removed

  • src/types.ts, src/board.ts, src/fen.ts — replaced by external packages.
  • FenState internal interface — replaced by Position class.
  • isInsufficientMaterial from detection.ts — delegated to position.isInsufficientMaterial.

[1.1.0] - 2026-03-15

Added

  • Game.isAttacked(square, color) — returns true if any piece of color attacks square. Matches chess.js semantics: pinned pieces still attack, own pieces count as attacked squares, no X-ray, same square returns false.

[1.0.0] - 2026-03-15

Changed

  • First stable release. No API changes from 0.1.1.

[0.1.1] - 2026-03-15

Changed

  • Switched internal board representation from a flat [64] array to the 0x88 [128] layout. Valid squares satisfy index & 0x88 === 0; the padding slots enable a single-instruction off-board check and the ATTACKS/RAYS lookup tables. No change to the public API.
  • isSquareAttackedBy now uses precomputed ATTACKS[240] and RAYS[240] tables (initialised at module load) instead of generating attack move lists and scanning them. Attack detection is O(1) per piece for non-sliding pieces and O(ray length) for sliding pieces with an early bitmask skip.
  • Game now lazily caches the legal move list and check flag per position. The cache is populated on the first call to moves(), isCheck(), isCheckmate(), isStalemate(), isDraw(), or isGameOver() from a given position, and invalidated on every move(), undo(), or redo(). Repeated queries from the same position are O(1) after the first call.
  • isInsufficientMaterial now correctly handles KB vs KB positions where all bishops are on the same square colour (previously returned false).
  • move() validates legality against the cached move list before clearing the cache, avoiding a redundant generateMoves call in the common moves() → move() pattern.
  • undo() and redo() check whether the history stack is empty before invalidating the cache, so no-op calls at the start/end of history do not evict the cache unnecessarily.
  • isDraw() in Game calls this.isStalemate() (cached) rather than delegating to the pure detection function, avoiding a redundant generateMoves call.

Added

  • OFF_BOARD = 0x88 exported from src/board.ts for use in moves.ts.
  • BENCHMARK_RESULTS.md — comparative benchmarks against chess.js@1.4.0 across all shared operations, plus a raw perft benchmark.
  • pnpm bench script — runs the comparison benchmark suite via Vitest bench.
  • vitest.config.ts — excludes benchmark files from coverage.
  • Extended test coverage:
    • Perft positions 2–7 from the chess programming wiki (depths 3–4), sourced from the chess.js test suite.
    • Perft depth 4 from the starting position (197,281 nodes).
    • Additional isCheckmate, isStalemate, isCheck, and isInsufficientMaterial positions from the chess.js test suite.
    • Regression: invalid castling rights in FEN must not crash isGameOver().

[0.1.0] - 2026-03-15

Added

  • Initial release with core chess game engine.
  • Game class — mutable, with move(), undo(), redo(), history(), moves(), get(), board(), fen(), turn(), isCheck(), isCheckmate(), isStalemate(), isDraw(), isGameOver().
  • Game.fromFen(fen) static factory for loading arbitrary positions.
  • Legal move generation for all piece types including castling, en passant, and promotion.
  • Game-state detection: check, checkmate, stalemate, 50-move rule, insufficient material, threefold repetition.
  • FEN parsing and serialisation (parseFen, serialiseFen, STARTING_FEN).
  • Zero runtime dependencies.