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 (don't worry, it's coming soon).

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();
...

Example Code

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);
}

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');

.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

.reset()

Reset the board to the initial starting position.

.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'

.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

.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'

.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'

.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

.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

.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' }

.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

.moves([ options ])

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.

.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

.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

.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)

.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

BUGS

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

TODO

add method to generate PGN (Portable Game Notation) output
add AI (basic alpha-beta search w/ primitive position evaluation)

Provide feedback

Saved searches

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README.md

README.md

chess.js

Example Code

API

Constructor: Chess([ fen ])

.load(fen)

.reset()

.fen()

.ascii()

.clear()

.turn()

.put(piece, square)

.get(square)

.remove(square)

.move(move)

.undo()

.moves([ options ])

.in_check()

.in_checkmate()

.in_draw()

.in_stalemate()

.in_threefold_repetition()

.insufficient_material()

.game_over()

.square_color(square)

BUGS

TODO

Files

README.md

Latest commit

History

README.md

File metadata and controls

chess.js

Example Code

API

Constructor: Chess([ fen ])

.load(fen)

.reset()

.fen()

.ascii()

.clear()

.turn()

.put(piece, square)

.get(square)

.remove(square)

.move(move)

.undo()

.moves([ options ])

.in_check()

.in_checkmate()

.in_draw()

.in_stalemate()

.in_threefold_repetition()

.insufficient_material()

.game_over()

.square_color(square)

BUGS

TODO