septian-bhoechie / chess.js

A Javascript chess library for chess move generation/validation, piece placement/movement, and check/checkmate/draw detection

chess.js

chess.js is a Javascript chess library that is used for chess move generation/validation, piece placement/movement, and check/checkmate/stalemate detection - basically everything but the AI.

chess.js has been extensively tested in node.js and most modern browsers.

Example Code

The code below plays a complete game of chess ... randomly.

var util = require('util'),
    ch =  require('./chess');

var chess = new ch.Chess();

while (!chess.game_over()) {
  util.puts('position: ' + chess.fen());
  var moves = chess.moves();
  var move = moves[Math.floor(Math.random() * moves.length)];
  chess.move(move);
  util.puts('move: ' + move);
}

Need a user interface? Try Chris Oakman's excellent ChessBoardJS library. The code below can be seen in action at ChessBoardJS - Random vs Random.

...
<link rel="stylesheet" href="css/chessboard-0.2.0.css" />
<script src="js/chess.js"></script>
<script src="js/chessboard-0.2.0.js"></script>
<script>
    var game = new Chess();
    var board = new ChessBoard('board', 'start');

    var random_move = function() {
        if (game.game_over()) return;
        var moves = game.moves();
        var move = moves[Math.floor(Math.random() * moves.length)];
        game.move(move);
        board.position(game.fen());
        window.setTimeout(random_move, 500);
    };

    window.setTimeout(random_move, 500);
</script>
...
<div id="board" style="width: 400px"></div>
...

chess.js is used in the projects below:

• 3D Hartwig Chess Set
• Chess in Javascript
• Multiplayer Chess
• EasyChess.com
• Reti Chess

API

Constructor: Chess([ fen ])

The Chess() constructor takes a optional parameter which specifies the board configuration in Forsyth-Edwards Notation.

// board defaults to the starting position when called with no parameters
var chess = new Chess();

// pass in a FEN string to load a particular position
var chess = new Chess('r1k4r/p2nb1p1/2b4p/1p1n1p2/2PP4/3Q1NB1/1P3PPP/R5K1 b - c3 0 19');

.ascii()

Returns a string containing an ASCII diagram of the current position.

var chess = new Chess();

// make some moves
chess.move('e4');
chess.move('e5');
chess.move('f4');

chess.ascii();
// -> '   +------------------------+
//      8 | r  n  b  q  k  b  n  r |
//      7 | p  p  p  p  .  p  p  p |
//      6 | .  .  .  .  .  .  .  . |
//      5 | .  .  .  .  p  .  .  . |
//      4 | .  .  .  .  P  P  .  . |
//      3 | .  .  .  .  .  .  .  . |
//      2 | P  P  P  P  .  .  P  P |
//      1 | R  N  B  Q  K  B  N  R |
//        +------------------------+
//          a  b  c  d  e  f  g  h'

.clear()

Clears the board.

chess.clear();
chess.fen();
// -> '8/8/8/8/8/8/8/8 w - - 0 1' <- empty board

.fen()

Returns the FEN string for the current position.

var chess = new Chess();

// make some moves
chess.move('e4');
chess.move('e5');
chess.move('f4');

chess.fen();
// -> 'rnbqkbnr/pppp1ppp/8/4p3/4PP2/8/PPPP2PP/RNBQKBNR b KQkq f3 0 2'

.game_over()

Returns true or false if the game has ended via checkmate, stalemate, or draw.

var chess = new Chess();
chess.game_over();
// -> false

chess.load('4k3/4P3/4K3/8/8/8/8/8 b - - 0 78');
chess.game_over();
// -> true (stalemate)

chess.load('rnb1kbnr/pppp1ppp/8/4p3/5PPq/8/PPPPP2P/RNBQKBNR w KQkq - 1 3');
chess.game_over();
// -> true (checkmate)

.get(square)

Returns the piece on the square:

chess.clear();
chess.put({ type: chess.PAWN, color: chess.BLACK }, 'a5') // put a black pawn on a5

chess.get('a5');
// -> { type: 'p', color: 'b' },
chess.get('a6');
// -> null

.history([ options ])

Returns a list containing the moves of the current game. Options is an optional parameter which may contain a 'verbose' flag. See .moves() for a description of the verbose move fields.

var chess = new Chess();
chess.move('e4');
chess.move('e5');
chess.move('f4');
chess.move('exf4');

chess.history();
// -> ['e4', 'e5', 'f4', 'exf4']

chess.history({ verbose: true });
// -> [{ color: 'w', from: 'e2', to: 'e4', flags: 'b', piece: 'p', san: 'e4' },
//     { color: 'b', from: 'e7', to: 'e5', flags: 'b', piece: 'p', san: 'e5' },
//     { color: 'w', from: 'f2', to: 'f4', flags: 'b', piece: 'p', san: 'f4' },
//     { color: 'b', from: 'e5', to: 'f4', flags: 'c', piece: 'p', captured: 'p', san: 'exf4' }]

.in_check()

Returns true or false if the side to move is in check.

var chess = new Chess('rnb1kbnr/pppp1ppp/8/4p3/5PPq/8/PPPPP2P/RNBQKBNR w KQkq - 1 3');
chess.in_check();
// -> true

.in_checkmate()

Returns true or false if the side to move has been checkmated.

var chess = new Chess('rnb1kbnr/pppp1ppp/8/4p3/5PPq/8/PPPPP2P/RNBQKBNR w KQkq - 1 3');
chess.in_checkmate();
// -> true

.in_draw()

Returns true or false if the game is drawn (50-move rule or insufficient material).

var chess = new Chess('4k3/4P3/4K3/8/8/8/8/8 b - - 0 78');
chess.in_draw();
// -> true

.in_stalemate()

Returns true or false if the side to move has been stalemated.

var chess = new Chess('4k3/4P3/4K3/8/8/8/8/8 b - - 0 78');
chess.in_stalemate();
// -> true

.in_threefold_repetition()

Returns true or false if the current board position has occurred three or more times.

var chess = new Chess('rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1');
// -> true
// rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq occurs 1st time
chess.in_threefold_repetition();
// -> false

chess.move('Nf3'); chess.move('Nf6') chess.move('Ng1'); chess.move('Ng8');
// rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq occurs 2nd time
chess.in_threefold_repetition();
// -> false

chess.move('Nf3'); chess.move('Nf6') chess.move('Ng1'); chess.move('Ng8');
// rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq occurs 3rd time
chess.in_threefold_repetition();
// -> true

.header()

Allows header information to be added to PGN output. Any number of key/value pairs can be passed to .header().

chess.header('White', 'Robert James Fischer');
chess.header('Black', 'Mikhail Tal');

// or

chess.header('White', 'Morphy', 'Black', 'Anderssen', 'Date', '1858-??-??');

.insufficient_material()

Returns true if the game is drawn due to insufficient material (K vs. K, K vs. KB, or K vs. KN); otherwise false.

var chess = new Chess('k7/8/n7/8/8/8/8/7K b - - 0 1');
chess.insufficient_material()
// -> true

.load(fen)

The board is cleared and the FEN string is loaded. Returns true if position was successfully loaded, otherwise false.

var chess = new Chess();
chess.load('4r3/8/2p2PPk/1p6/pP2p1R1/P1B5/2P2K2/3r4 w - - 1 45');
// -> true

chess.load('4r3/8/X12XPk/1p6/pP2p1R1/P1B5/2P2K2/3r4 w - - 1 45');
// -> false, bad piece X

.load_pgn(pgn, [ options ])

Load the moves of a game stored in Portable Game Notation. Options is a optional parameter that contains a 'newline_char' denoting the line delimiter (the default delimiter is '\r?\n', optional carriage return with newline). Returns true if the PGN was parsed successfully, otherwise false.

var chess = new Chess();
pgn = ['[Event "Casual Game"]',
       '[Site "Berlin GER"]',
       '[Date "1852.??.??"]',
       '[EventDate "?"]',
       '[Round "?"]',
       '[Result "1-0"]',
       '[White "Adolf Anderssen"]',
       '[Black "Jean Dufresne"]',
       '[ECO "C52"]',
       '[WhiteElo "?"]',
       '[BlackElo "?"]',
       '[PlyCount "47"]',
       '',
       '1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.b4 Bxb4 5.c3 Ba5 6.d4 exd4 7.O-O',
       'd3 8.Qb3 Qf6 9.e5 Qg6 10.Re1 Nge7 11.Ba3 b5 12.Qxb5 Rb8 13.Qa4',
       'Bb6 14.Nbd2 Bb7 15.Ne4 Qf5 16.Bxd3 Qh5 17.Nf6+ gxf6 18.exf6',
       'Rg8 19.Rad1 Qxf3 20.Rxe7+ Nxe7 21.Qxd7+ Kxd7 22.Bf5+ Ke8',
       '23.Bd7+ Kf8 24.Bxe7# 1-0'];

chess.load_pgn(pgn.join('\n'));
// -> true

chess.fen()
// -> 1r3kr1/pbpBBp1p/1b3P2/8/8/2P2q2/P4PPP/3R2K1 b - - 0 24

chess.ascii()
// -> '  +------------------------+
//     8 | .  r  .  .  .  k  r  . |
//     7 | p  b  p  B  B  p  .  p |
//     6 | .  b  .  .  .  P  .  . |
//     5 | .  .  .  .  .  .  .  . |
//     4 | .  .  .  .  .  .  .  . |
//     3 | .  .  P  .  .  q  .  . |
//     2 | P  .  .  .  .  P  P  P |
//     1 | .  .  .  R  .  .  K  . |
//       +------------------------+
//         a  b  c  d  e  f  g  h'

.move(move)

Attempts to make a move on the board, returning a move object if the move was legal, otherwise null. The .move function can be called two ways, by passing a string in Standard Algebraic Notation (SAN):

var chess = new Chess();

chess.move('e4')
// -> { color: 'w', from: 'e2', to: 'e4', flags: 'b', piece: 'p', san: 'e2' }

chess.move('nf6') // SAN is case sensitive!!
// -> null

chess.move('Nf6')
// -> { color: 'b', from: 'g8', to: 'f6', flags: 'n', piece: 'n', san: 'Nf6' }

Or by passing .move() a move object (only the 'to', 'from', and when necessary 'promotion', fields are needed):

var chess = new Chess();

chess.move({ from: 'g2', to: 'g3' });
// -> { color: 'w', from: 'g2', to: 'g3', flags: 'n', piece: 'p', san: 'g3' }

.moves([ options ])

Returns a list of legals moves from the current position. The function takes an optional parameter which controls the single-square move generation and verbosity.

var chess = new Chess();
chess.moves();
// -> ['a3', 'a4', 'b3', 'b4', 'c3', 'c4', 'd3', 'd4', 'e3', 'e4',
//     'f3', 'f4', 'g3', 'g4', 'h3', 'h4', 'Na3', 'Nc3', 'Nf3', 'Nh3']

chess.moves({square: 'e2'});
// -> ['e3', 'e4']

chess.moves({square: 'e9'}); // invalid square
// -> []

chess.moves({ verbose: true });
// -> [{ color: 'w', from: 'a2', to: 'a3',
//       flags: 'n', piece: 'p', san 'a3'
//       # a captured: key is included when the move is a capture
//       # a promotion: key is included when the move is a promotion
//     },
//     ...
//     ]

The piece, captured, and promotion fields contain the lowercase representation of the applicable piece.

The flags field in verbose mode may contain one or more of the following values:

• 'n' - a non-capture
• 'b' - a pawn push of two squares
• 'e' - an en passant capture
• 'c' - a standard capture
• 'p' - a promotion
• 'k' - kingside castling
• 'q' - queenside castling

A flag of 'pc' would mean that a pawn captured a piece on the 8th rank and promoted.

.pgn([ options ])

Returns the game in PGN format. Options is an optional parameter which may include max width and/or a newline character settings.

var chess = new Chess();
chess.header('White', 'Plunky', 'Black', 'Plinkie');
chess.move('e4');
chess.move('e5');
chess.move('Nc3');
chess.move('Nc6');

chess.pgn({ max_width: 5, newline_char: '<br />' });
// -> '[White "Plunky"]<br />[Black "Plinkie"]<br /><br />1. e4 e5<br />2. Nc3 Nc6'

.put(piece, square)

Place a piece on square where piece is an object with the form { type: ..., color: ... }. Returns true if piece was successfully placed, otherwise false.

chess.clear();

chess.put({ type: chess.PAWN, color: chess.BLACK }, 'a5') // put a black pawn on a5
// -> true
chess.put({ type: 'k', color: 'w' }, 'h1') // shorthand
// -> true

chess.fen();
// -> '8/8/8/p7/8/8/8/7K w - - 0 0'

.remove(square)

Remove and return the piece on square.

chess.clear();
chess.put({ type: chess.PAWN, color: chess.BLACK }, 'a5') // put a black pawn on a5
chess.put({ type: chess.KING, color: chess.WHITE }, 'h1') // put a white king on h1

chess.remove('a5');
// -> { type: 'p', color: 'b' },
chess.remove('h1');
// -> { type: 'k', color: 'w' },
chess.remove('e1');
// -> null

.reset()

Reset the board to the initial starting position.

.square_color(square)

Returns the color of the square ('light' or 'dark').

var chess = Chess();
chess.square_color('h1')
// -> 'light'
chess.square_color('a7')
// -> 'dark'
chess.square_color('bogus square')
// -> null

.turn()

Returns the current side to move.

chess.load('rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1')
chess.turn()
// -> 'b'

.undo()

Takeback the last half-move, returning a move object if successful, otherwise null.

var chess = new Chess();

chess.fen();
// -> 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1'
chess.move('e4');
chess.fen();
// -> 'rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1'

chess.undo();
// -> { color: 'w', from: 'e2', to: 'e4', flags: 'b', piece: 'p', san: 'e4' }
chess.fen();
// -> 'rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1'
chess.undo();
// -> null

.validate_fen(fen):

Returns a validation object specifying validity or the errors found within the FEN string.

chess.validate_fen('2n1r3/p1k2pp1/B1p3b1/P7/5bP1/2N1B3/1P2KP2/2R5 b - - 4 25');
// -> { valid: true, error_number: 0, error: 'No errors.' }

chess.validate_fen('4r3/8/X12XPk/1p6/pP2p1R1/P1B5/2P2K2/3r4 w - - 1 45');
// -> { valid: false, error_number: 9,
//     error: '1st field (piece positions) is invalid [invalid piece].' }

CONTRIBUTORS

Special thanks to the following developers for their patches and contributions (alphabetically):

• Steve Bragg
• E. Azer Koçulu
• Falco Nogatz
• jdponomarev
• David Moises Paz Reyes
• Raminder Singh
• Stiff
• Seb Vincent
• Linmiao Xu

Musical support provided by:

• The Grateful Dead
• Umphrey's McGee

BUGS

• The en passant square and castling flags aren't adjusted when using the put/remove functions (workaround: use .load() instead)

TODO

• Add AI (basic alpha-beta search w/ primitive position evaluation). The AI should probably be internal to the underlying Chess() object to take full advantage of 0x88 move generation.
• Add jQuery chessboard widget. (see widget branch for prototype)
• Investigate the use of piece lists (this may shave a few cycles off generate_moves() and attacked())