node-chess - the algebraic chess engine

node-chess is an algebraic notation driven chess engine that can validate board position and produce a list of viable moves (notated).

Features

• Accepts moves in algebraic notation
• Lists valid moves in algebraic notation
• Fuzzy algebraic notation parsing
• En Passant validation
• 3-fold repetition detection
• Stalemate detection
• Check detection
• Checkmate detection
• Undo moves easily
• Easily readable object structure
• High unit test coverage

Installation

npm install chess

Public API

Create a new game

import chess from 'chess';

// create a game client
const gameClient = chess.create();
let move, status;

// capture events
gameClient.on('check', (attack) => {
  // get more details about the attack on the King
  console.log(attack);
});

// look at the status and valid moves
status = gameClient.getStatus();

// make a move
move = gameClient.move('a4');

// look at the status again after the move to see
// the opposing side's available moves
status = gameClient.getStatus();

PGN (Portable Game Format) Algebraic Game Client

To ensure the notation returned is safe for PGN, you must supply PGN as an option in the call to create:

import chess from 'chess';

// create a game client
const gameClient = chess.create({ PGN : true });
let move, status;

// look at the status and valid moves
status = gameClient.getStatus();

// make a move
move = gameClient.move('a4');

// look at the status again after the move to see
// the opposing side's available moves
status = gameClient.getStatus();

Game Events

The game client (both algebraic, simple) emit a number of events when scenarios occur on the board over the course of a match.

import chess from 'chess';

// create a game client
const gameClient = chess.create({ PGN : true });

// when a capture occurs
gameClient.on('capture', (move) => {
  console.log('A piece has been captured!');
  console.log(move);
});

// when a castle occurs
gameClient.on('castle', (move) => {
  console.log('A castle has occured!');
  console.log(move);
});

// when a King is placed in check
gameClient.on('check', (attack) => {
  console.log('The King is under attack!');
  console.log(attack);
});

// when King is placed in checkmate
gameClient.on('checkmate', (attack) => {
  console.log('The game has ended due to checkmate!');
  console.log(attack);
});

// when en Passant occurs
gameClient.on('enPassant', (move) => {
  console.log('An en Passant has occured!');
  console.log(move);
});

// when a move occurs on the board
gameClient.on('move', (move) => {
  console.log('A piece was moved!');
  console.log(move);
});

// when a Pawn promotion occurs
gameClient.on('promote', (square) => {
  console.log('A Pawn has been promoted!');
  console.log(square);
});

// when an undo function is called on a move
gameClient.on('undo', (move) => {
  console.log('A previous move was undone!');
  console.log(move);
});

The capture Event

The capture event is emitted when a piece has been captured during game play. The capture event data is the same as the move object that is provided as a response to gameClient.move().

The check Event

The check event is emitted for each attack on a King that occurs on the board. In the event a single move results in multiple pieces putting a King in check, multiple check events will be emitted, one for each attack.

The attack Object

The attack object contains the attacking square and the King square. The properties of the attack object are:

• attackingSquare - The square object from which the attacker originates which includes the piece conducting the attack
• kingSquare - The square object representing the King that is under attack

{
  attackingSquare : {
    file: 'f',
    rank: 6,
    piece: {
      moveCount: 3,
      side: {
        name: 'white'
      },
      type: 'knight',
      notation: 'N'
    }
  },
  kingSquare : {
    file: 'e',
    rank: 8,
    piece: {
      moveCount: 0,
      side: {
        name: 'black'
      },
      type: 'king',
      notation: 'K'
    }
  }
}

The checkmate Event

The checkmate event is emitted when checkmate has been detected on the board. The checkmate event data is the same as the attack object that is provided for the check event.

The castle Event

The castle event is emitted when a castle move occurs on the board. The castle event data is the move object that is also returned when performing a gameClient.move().

The enPassant Event

When en Passant occurs, the enPassant event is emitted. The enPassant event data is the move object that is also returned when performing a gameClient.move().

The move Event

Any time a move occurs on the board, the move event is emitted. The enPassant event data is the move object that is also returned when performing a gameClient.move().

The promote Event

When a Pawn promotion occurs, the promote event is emitted. The promote event data is the Square object upon which the newly promoted piece resides, which looks as follows:

{
  file: 'a',
  piece: {
    moveCount: 2,
    notation: 'R',
    side: {
      name: 'white'
    },
    type: 'rook' },
  rank: 8
}

The undo Event

The undo event is emitted when a previous move that occured on the board is reversed using the undo method. The undo event data is the same move object that is also returned when performing a gameClient.move().

The gameClient.move() Function

From the above example, the response object that is returned when calling chess.move() looks like the following:

{
  move: {
    // the captured piece (if capture occurred)
    capturedPiece: null,
    // was the move a castle?
    castle: false,
    // was the move en Passant?
    enPassant: false,
    // tje square a piece was moved to
    postSquare: {
      file: 'a',
      rank: 4,
      piece: {
        moveCount: 1,
        side: {
          name: 'white'
        },
        type: 'pawn',
        notation: 'R'
      }
    },
    // the square that the piece came from
    prevSquare: {
      file: 'a',
      rank: 2,
      piece: null
    }
  },
  // undo() can be used to back out the previous move
  undo: __function__
}

The move Object

The move object contains a collection of properties and an undo function pointer. The five properties of the move object are:

• capturedPiece - If a piece was captured during the move, it will be represented here.
• castle - If the move was a castle, this will be set to true, otherwise false.
• enPassant - If the move was en passant, this will be set to true, otherwise false.
• postSquare - The destination square object for the move.
• prevSquare - The square object from which the move was originated.

The undo() Function

To back out the move:

move.undo();

The gameClient.getStatus() Function

The status object is as follows (abbreviated in parts to improve readability):

{
  // this is the top level board
  board: {
    // an array of all squares on the board
    squares: [{
        file: 'a',
        rank: 1,
        piece: {
          moveCount: 0,
          side: {
            name: 'white'
          },
          type: 'rook',
          notation: 'R'
        }
      },
      /* the rest of the squares... */
    ]
  },
  isCheck: false, // is the King currently in check?
  isCheckmate: false, // is the King currently in checkmate?
  isRepetition: false, // has 3-fold repetition occurred?
  isStalemate: false, // is the board in stalemate?
  // all possible moves (notated) with details for each move
  notatedMoves: {
    a3: {
      src: {
        file: 'a'
        rank: 2,
        piece: {
          moveCount: 0,
          side: {
            name: 'white'
          },
          type: 'pawn',
          notation: 'R'
        }
      },
      dest: {
        file: 'a',
        rank: 3,
        piece: null
      }
    },
    /* the rest of the available moves... */
  }
}

The status Object

The status object returned via the getStatus() function call contains several Object properties:

• board - The underlying board Object which contains the collection of squares.
• isCheck - If the status of the board is check, this will be true.
• isCheckmate - If the status of the board is checkmate, this will be true. Additionally, the notatedMoves property will be empty.
• isRepetition - If 3-fold repetition has occurred, this will be true. The notatedMoves property will not be empty as the game can technically continue.
• isStalemate - If the board is in stalemate, this will be set to true.
• notatedMoves - A hash containing all available moves on the board.

The status.notatedMoves Object

Each object within the notatedMoves hash represents a possible move. The key to the hash is the algebraic notation of the move. The value for each key in the hash has two properties:

• src - The starting square (which contains a piece) of the move
• dest - The destination square of the move

The following code is an example of how to iterate the available notated moves for the game.

import chess from 'chess';
const gameClient = chess.create();

let
  i = 0,
  key = '',
  status = gameClient.getStatus();

Object.keys(status.notatedMoves).map((key, index) => {
  console.log(status.notatedMoves[key]);
  return { ...status.notatedMoves[key], key };
});

Example usage

The following usage of the code is playing out the 3rd game in the series between Fischer and Petrosian in Buenos Aires, 1971. The game ended a draw due to 3 fold repetition.

import chess from 'chess';
const util = require('util');

const gameClient = chess.create();

// 1. e4 e6
gameClient.move('e4');
gameClient.move('e6');
// 2. d4 d5
gameClient.move('d4');
gameClient.move('d5');
// 3. Nc3 Nf6
gameClient.move('Nc3');
gameClient.move('Nf6');
// 4. Bg5 dxe4
gameClient.move('Bg5');
gameClient.move('dxe4');
// 5. Nxe4 Be7
gameClient.move('Nxe4');
gameClient.move('Be7');
// 6. Bxf6 gxf6
gameClient.move('Bxf6');
gameClient.move('gxf6');
// 7. g3 f5
gameClient.move('g3');
gameClient.move('f5');
// 8. Nc3 Bf6
gameClient.move('Nc3');
gameClient.move('Bf6');
// 9. Nge2 Nc6
gameClient.move('Nge2');
gameClient.move('Nc6');
// 10. d5 exd5
gameClient.move('d5');
gameClient.move('exd5');
// 11. Nxd5 Bxb2
gameClient.move('Nxd5');
gameClient.move('Bxb2');
// 12. Bg2 O-O
gameClient.move('Bg2');
gameClient.move('0-0');
// 13. O-O Bh8
gameClient.move('0-0');
gameClient.move('Bh8');
// 14. Nef4 Ne5
gameClient.move('Nef4');
gameClient.move('Ne5');
// 15. Qh5 Ng6
gameClient.move('Qh5');
gameClient.move('Ng6');
// 16. Rad1 c6
gameClient.move('Rad1');
gameClient.move('c6');
// 17. Ne3 Qf6
gameClient.move('Ne3');
gameClient.move('Qf6');
// 18. Kh1 Bg7
gameClient.move('Kh1');
gameClient.move('Bg7');
// 19. Bh3 Ne7
gameClient.move('Bh3');
gameClient.move('Ne7');
// 20. Rd3 Be6
gameClient.move('Rd3');
gameClient.move('Be6');
// 21. Rfd1 Bh6
gameClient.move('Rfd1');
gameClient.move('Bh6');
// 22. Rd4 Bxf4
gameClient.move('Rd4');
gameClient.move('Bxf4');
// 23. Rxf4 Rad8
gameClient.move('Rxf4');
gameClient.move('Rad8');
// 24. Rxd8 Rxd8
gameClient.move('Rxd8');
gameClient.move('Rxd8');
// 25. Bxf5 Nxf5
gameClient.move('Bxf5');
gameClient.move('Nxf5');
// 26. Nxf5 Rd5
gameClient.move('Nxf5');
gameClient.move('Rd5');
// 27. g4 Bxf5
gameClient.move('g4');
gameClient.move('Bxf5');
// 28. gxf5 h6
gameClient.move('gxf5');
gameClient.move('h6');
// 29. h3 Kh7
gameClient.move('h3');
gameClient.move('Kh7');
// 30. Qe2 Qe5
gameClient.move('Qe2');
gameClient.move('Qe5');
// 31. Qh5 Qf6
gameClient.move('Qh5');
gameClient.move('Qf6');
// 32. Qe2 Re5
gameClient.move('Qe2');
gameClient.move('Re5');
// 33. Qd3 Rd5
gameClient.move('Qd3');
gameClient.move('Rd5');
// 34. Qe2
gameClient.move('Qe2');

console.log(util.inspect(gameClient.getStatus(), false, 7));

Output

The above code produces the following output:

{
  board: {
    squares: [
      { file: 'a', rank: 1, piece: null },
      { file: 'b', rank: 1, piece: null },
      { file: 'c', rank: 1, piece: null },
      { file: 'd', rank: 1, piece: null },
      { file: 'e', rank: 1, piece: null },
      { file: 'f', rank: 1, piece: null },
      { file: 'g', rank: 1, piece: null },
      { file: 'h',
        rank: 1,
        piece:
          { moveCount: 2,
            side: { name: 'white' },
            type: 'king',
            notation: 'K' } },
      { file: 'a',
        rank: 2,
        piece:
          { moveCount: 0,
            side: { name: 'white' },
            type: 'pawn',
            notation: '' } },
      { file: 'b', rank: 2, piece: null },
      { file: 'c',
        rank: 2,
        piece:
          { moveCount: 0,
            side: { name: 'white' },
            type: 'pawn',
            notation: '' } },
      { file: 'd', rank: 2, piece: null },
      { file: 'e',
        rank: 2,
        piece:
          { moveCount: 6,
            side: { name: 'white' },
            type: 'queen',
            notation: 'Q' } },
      { file: 'f',
        rank: 2,
        piece:
          { moveCount: 0,
            side: { name: 'white' },
            type: 'pawn',
            notation: '' } },
      { file: 'g', rank: 2, piece: null },
      { file: 'h', rank: 2, piece: null },
      { file: 'a', rank: 3, piece: null },
      { file: 'b', rank: 3, piece: null },
      { file: 'c', rank: 3, piece: null },
      { file: 'd', rank: 3, piece: null },
      { file: 'e', rank: 3, piece: null },
      { file: 'f', rank: 3, piece: null },
      { file: 'g', rank: 3, piece: null },
      { file: 'h',
        rank: 3,
        piece:
          { moveCount: 1,
            side: { name: 'white' },
            type: 'pawn',
            notation: '' } },
      { file: 'a', rank: 4, piece: null },
      { file: 'b', rank: 4, piece: null },
      { file: 'c', rank: 4, piece: null },
      { file: 'd', rank: 4, piece: null },
      { file: 'e', rank: 4, piece: null },
      { file: 'f',
        rank: 4,
        piece:
          { moveCount: 4,
            side: { name: 'white' },
            type: 'rook',
            notation: 'R' } },
      { file: 'g', rank: 4, piece: null },
      { file: 'h', rank: 4, piece: null },
      { file: 'a', rank: 5, piece: null },
      { file: 'b', rank: 5, piece: null },
      { file: 'c', rank: 5, piece: null },
      { file: 'd',
        rank: 5,
        piece:
          { moveCount: 4,
            side: { name: 'black' },
            type: 'rook',
            notation: 'R' } },
      { file: 'e', rank: 5, piece: null },
      { file: 'f',
        rank: 5,
        piece:
          { moveCount: 3,
            side: { name: 'white' },
            type: 'pawn',
            notation: '' } },
      { file: 'g', rank: 5, piece: null },
      { file: 'h', rank: 5, piece: null },
      { file: 'a', rank: 6, piece: null },
      { file: 'b', rank: 6, piece: null },
      { file: 'c',
        rank: 6,
        piece:
          { moveCount: 1,
            side: { name: 'black' },
            type: 'pawn',
            notation: '' } },
      { file: 'd', rank: 6, piece: null },
      { file: 'e', rank: 6, piece: null },
      { file: 'f',
        rank: 6,
        piece:
          { moveCount: 3,
            side: { name: 'black' },
            type: 'queen',
            notation: 'Q' } },
      { file: 'g', rank: 6, piece: null },
      { file: 'h',
        rank: 6,
        piece:
          { moveCount: 1,
            side: { name: 'black' },
            type: 'pawn',
            notation: '' } },
      { file: 'a',
        rank: 7,
        piece:
          { moveCount: 0,
            side: { name: 'black' },
            type: 'pawn',
            notation: '' } },
      { file: 'b',
        rank: 7,
        piece:
          { moveCount: 0,
            side: { name: 'black' },
            type: 'pawn',
            notation: '' } },
      { file: 'c', rank: 7, piece: null },
      { file: 'd', rank: 7, piece: null },
      { file: 'e', rank: 7, piece: null },
      { file: 'f',
        rank: 7,
        piece:
          { moveCount: 0,
            side: { name: 'black' },
            type: 'pawn',
            notation: '' } },
      { file: 'g', rank: 7, piece: null },
      { file: 'h',
        rank: 7,
        piece:
          { moveCount: 2,
            side: { name: 'black' },
            type: 'king',
            notation: 'K' } },
      { file: 'a', rank: 8, piece: null },
      { file: 'b', rank: 8, piece: null },
      { file: 'c', rank: 8, piece: null },
      { file: 'd', rank: 8, piece: null },
      { file: 'e', rank: 8, piece: null },
      { file: 'f', rank: 8, piece: null },
      { file: 'g', rank: 8, piece: null },
      { file: 'h', rank: 8, piece: null }
    ],
  },
  isCheck: false,
  isCheckmate: false,
  isRepetition: true,
  isStalemate: false,
  notatedMoves:
    { Rd4:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'd', rank: 4, piece: null } },
      Rd3:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'd', rank: 3, piece: null } },
      Rd2:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'd', rank: 2, piece: null } },
      Rd1:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'd', rank: 1, piece: null } },
      Rd6:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'd', rank: 6, piece: null } },
      Rd7:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'd', rank: 7, piece: null } },
      Rd8:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'd', rank: 8, piece: null } },
      Rc5:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'c', rank: 5, piece: null } },
      Rb5:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'b', rank: 5, piece: null } },
      Ra5:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'a', rank: 5, piece: null } },
      Re5:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest: { file: 'e', rank: 5, piece: null } },
      Rxf5:
      { src:
          { file: 'd',
            rank: 5,
            piece:
            { moveCount: 4,
              side: { name: 'black' },
              type: 'rook',
              notation: 'R' } },
        dest:
          { file: 'f',
            rank: 5,
            piece:
            { moveCount: 3,
              side: { name: 'white' },
              type: 'pawn',
              notation: '' } } },
      c5:
      { src:
          { file: 'c',
            rank: 6,
            piece:
            { moveCount: 1,
              side: { name: 'black' },
              type: 'pawn',
              notation: '' } },
        dest: { file: 'c', rank: 5, piece: null } },
      Qxf5:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest:
          { file: 'f',
            rank: 5,
            piece:
            { moveCount: 3,
              side: { name: 'white' },
              type: 'pawn',
              notation: '' } } },
      Qe6:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'e', rank: 6, piece: null } },
      Qd6:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'd', rank: 6, piece: null } },
      Qg6:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'g', rank: 6, piece: null } },
      Qe7:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'e', rank: 7, piece: null } },
      Qd8:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'd', rank: 8, piece: null } },
      Qg5:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'g', rank: 5, piece: null } },
      Qh4:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'h', rank: 4, piece: null } },
      Qe5:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'e', rank: 5, piece: null } },
      Qd4:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'd', rank: 4, piece: null } },
      Qc3:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'c', rank: 3, piece: null } },
      Qb2:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'b', rank: 2, piece: null } },
      Qa1:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'a', rank: 1, piece: null } },
      Qg7:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'g', rank: 7, piece: null } },
      Qh8:
      { src:
          { file: 'f',
            rank: 6,
            piece:
            { moveCount: 3,
              side: { name: 'black' },
              type: 'queen',
              notation: 'Q' } },
        dest: { file: 'h', rank: 8, piece: null } },
      h5:
      { src:
          { file: 'h',
            rank: 6,
            piece:
            { moveCount: 1,
              side: { name: 'black' },
              type: 'pawn',
              notation: '' } },
        dest: { file: 'h', rank: 5, piece: null } },
      a6:
      { src:
          { file: 'a',
            rank: 7,
            piece:
            { moveCount: 0,
              side: { name: 'black' },
              type: 'pawn',
              notation: '' } },
        dest: { file: 'a', rank: 6, piece: null } },
      a5:
      { src:
          { file: 'a',
            rank: 7,
            piece:
            { moveCount: 0,
              side: { name: 'black' },
              type: 'pawn',
              notation: '' } },
        dest: { file: 'a', rank: 5, piece: null } },
      b6:
      { src:
          { file: 'b',
            rank: 7,
            piece:
            { moveCount: 0,
              side: { name: 'black' },
              type: 'pawn',
              notation: '' } },
        dest: { file: 'b', rank: 6, piece: null } },
      b5:
      { src:
          { file: 'b',
            rank: 7,
            piece:
            { moveCount: 0,
              side: { name: 'black' },
              type: 'pawn',
              notation: '' } },
        dest: { file: 'b', rank: 5, piece: null } },
      Kh8:
      { src:
          { file: 'h',
            rank: 7,
            piece:
            { moveCount: 2,
              side: { name: 'black' },
              type: 'king',
              notation: 'K' } },
        dest: { file: 'h', rank: 8, piece: null } },
      Kg7:
      { src:
          { file: 'h',
            rank: 7,
            piece:
            { moveCount: 2,
              side: { name: 'black' },
              type: 'king',
              notation: 'K' } },
        dest: { file: 'g', rank: 7, piece: null } },
      Kg8:
      { src:
          { file: 'h',
            rank: 7,
            piece:
            { moveCount: 2,
              side: { name: 'black' },
              type: 'king',
              notation: 'K' } },
        dest: { file: 'g', rank: 8, piece: null } } } }