@chess-fu/fen-parser

SYNOPSIS

This is a small lightweight chess FEN parser based largely on regex. It unpacks the FEN into discrete properties which can be modified and then turned back into a new FEN via the toString method.

VALIDATION

The following aspects of the FEN are validated:

The FEN must acurately represents an 8x8 board.
The pieces must be in the standard prnbqk set.
The player field is either set to 'w' or 'b'.
The castle grants may be none ('-') or contain 'k' or 'q' or any file 'abcdefgh' for Chess960 support.
The en passant must be none ('-') or an 'abcdefgh' file, followed by either 3 or 6 for rank.
The half-move clock must be 1 to 3 digits long.
The move number must be 1 to 4 digits long.

Due to some irregular FENs in use, the addition case of a missing en passant code followed by 0 0 will be allowed. In this case the FenParser will report as if the ending was - 0 1 and the toString method will reflect that change. Thank you chess.com for that :D

INSTALL

npm install --save @chess-fu/fen-parser

Not much else to it.

USAGE

Basic usage:

  function () {
    assert.isTrue(FenParser.isFen('rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1'));
    assert.isFalse(FenParser.isFen('xxxxx/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1'));
    const fen = new FenParser('rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1');
    assert.isTrue(fen.isValid);
    assert.equal(fen.positions, 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR');
    assert.equal(fen.ranks[0], 'rnbqkbnr');
    assert.equal(fen.ranks[1], 'pppppppp');
    assert.equal(fen.ranks[2], '--------');
    assert.equal(fen.ranks[3], '--------');
    assert.equal(fen.ranks[4], '--------');
    assert.equal(fen.ranks[5], '--------');
    assert.equal(fen.ranks[6], 'PPPPPPPP');
    assert.equal(fen.ranks[7], 'RNBQKBNR');
    assert.equal(fen.turn, 'w');
    assert.equal(fen.castles, 'KQkq');
    assert.equal(fen.enpass, '-');
    assert.equal(fen.halfmoveClock, 0);
    assert.equal(fen.moveNumber, 1);
    assert.equal(fen.toString(), 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1');
  }

Members

static isFen(string): boolean Returns true if the the parts of the FEN appear valid at a glance. Use the isValid member to verify run-length encoding.

get isValid: boolean Returns true if the FEN provided to the constructor was validated and represented the full 8x8 board.

get positions: string Gets the encoded version of the ranks, use the ranks property to modify.

ranks: string[] Gets or sets the unencoded rank & file position of pieces using a dash '-' for an empty square.

turn: 'w' | 'b' Gets or sets the color of the player who should make the next move.

castles: string Gets or sets the valid sides (kqKQ) or files (abcdefghABCDEFGH) valid for castling.

enpass: string Gets or sets the currently possible en passant square in file+rank notation, or - for none.

halfmoveClock: number Gets or sets the number of halfmoves since the last capture or pawn advance.

moveNumber: number Gets or sets the number of the full move. It starts at 1, and is incremented after Black's move.

toString(): string Returns the re-assembled FEN string.

hasPiece(string): boolean Return true if the piece (character) is found on the board.

counts(): map(string -> number) Returns a map object for each piece type found to the number of occurrences.