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.
Using chess.js in a browser is straight-forward:
<script type="text/javascript" src="chess.js"></script>
<script type="text/javascript">
var chess = new Chess();
...
</script>
Using chess.js in node.js is equally easy:
var ch = require('/chess.js')
var chess = new ch.Chess();
...
The code below plays a complete game of chess ... randomly.
var sys = require('sys'),
ch = require('./chess');
var chess = new ch.Chess();
while (!chess.game_over()) {
sys.puts('position: ' + chess.fen());
var moves = chess.moves();
var move = moves[Math.floor(Math.random() * moves.length)];
chess.move(move);
sys.puts('move: ' + move);
}
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');
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
Reset the board to the initial starting position.
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'
Allows header information to be added to PGN output. Any number of key/values can be passed to .info(). See .pgn() for example.
Returns the game in PGN format. Options is an object that can include max width and/or a newline character.
var chess = new Chess();
chess.info("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'
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'
Clears the board.
chess.clear();
chess.fen();
// -> '8/8/8/8/8/8/8/8 w - - 0 1' <- empty board
Returns the current side to move.
chess.load('rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1')
chess.turn()
// -> 'b'
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'
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
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
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' }
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
Returns a list of all legal moves from the current position. The function be passed a options hash which controls the verbosity of the return values (this may change in the future).
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({ 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.
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
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
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
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
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
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
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)
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
Special thanks to the following developers for their patches and contributions:
Musical support provided by:
- the en passant square and castling flags aren't adjusted when using the put/remove functions (workaround: use .load() instead)
- add method to input PGN
- add AI (basic alpha-beta search w/ primitive position evaluation)
- add jQuery chessboard widget
- investigate the use of piece lists (this may shave a few cycles off generate_moves() and attacked())