isepic-chess.js is a chess utility library written in JavaScript, it provides features like legal moves calculation, FEN validation, SAN parsing, etc. (see: Features).

Flexibility: it strives to be flexible (inspired by JavaScript) and attempts to make things work without easily giving up and throwing errors.

Code coverage: the extra flexibility adds extra complexity and paths to be tested, but despite this, the code coverage is 98~% (as of v6.0.0).

Perft-tested: each release is tested against known Perft positions to ensure that the move generation tree of legal moves do not vary from the correct count.

UI-less: all the bloating code that a user interface brings is completely separated into this other project: Isepic Chess UI.

Dependency-less: does not depend on any other library.

:pushpin: Table of contents

• isepic-chess.js
• Table of contents
• Installation
• Node.js example
• Demo
• Features
• Documentation
• Copyright and license

:computer_mouse: Installation

# NPM
npm install isepic-chess

Then: const {Ic} = require("isepic-chess");

# Web browser
<script src="./isepic-chess.js"></script>

The variable Ic will be added to window.

:green_heart: Node.js example

const { Ic } = require('isepic-chess');

var example_pgn = `[Event "m1 London"]
[Site "?"]
[Date "1861.07.??"]
[Round "9"]
[White "Kolisch, Ignatz"]
[Black "Anderssen, Adolf"]
[Result "0-1"]
[Annotator "JvR"]
[SetUp "1"]
[FEN "5r1k/pp4pp/3r3q/8/3PpP1P/1P2NbP1/PB1Q3K/R7 b - - 0 30"]
[PlyCount "13"]
[EventDate "1861.??.??"]

30... Rxf4 $1 {Anderssen starts fireworks.} 31. Qe1 (31.gxf4 $2 Qxh4+ 32.Kg1
Rg6+) 31... Rg6 (31...Rxh4+ $1 32.gxh4 Rg6 $1) 32. Bc1 (32.Ng2 $1) 32... Rxh4+
$1 33. gxh4 Qf4+ 34. Kh3 Bg2+ $1 35. Nxg2 Qf3+ 36. Kh2 Qxg2# { Anderssen won
the match by this mate (+4, =2, -3).} 0-1`;

var board = Ic.initBoard({
  pgn: example_pgn,
});

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

console.log(board.fen);
// "7k/pp4pp/6r1/8/3Pp2P/1P6/P5qK/R1B1Q3 w - - 0 37"

var fen_arr = [
  'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1',
  'r1bqk2r/pppp1pbp/2n2n2/4p3/5p2/2N3PN/PPPPP1BP/R1BQK2R w KQkq - 2 8',
  'r2qkb1r/pbp1p1p1/1pnp1n1p/5p2/4P2P/5NP1/PPPPKPB1/RNBQR3 w kq - 0 8',
  'rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq - 0 1',
  'r2qkbnr/ppp4p/2np1p2/4p3/3PP3/P2B1N2/1PP2PpP/RNBQ1RK1 b kq - 1 11',
];

/* transform each FEN into arrays with their legal UCI moves for the g2 square */
var mapped = fen_arr.map((fen) => Ic.fenApply(fen, 'legalSanMoves', ['g2']));

console.log(mapped);
// [
//  ["g2g3", "g2g4"],
//  ["g2f1", "g2f3", "g2e4", "g2d5", "g2c6"],
//  ["g2h3", "g2h1", "g2f1"],
//  [],
//  ["g2f1n", "g2f1b", "g2f1r", "g2f1q"]
// ]

/* get only the positions where the white king is not in its original square */
var filtered = fen_arr.filter((fen) => {
  var obj, rtn;

  rtn = false;
  obj = Ic.fenGet(fen, 'w');

  if (obj) {
    rtn = obj.w.kingBos !== 'e1';
  }

  return rtn;
});

console.log(filtered);
// [
//  "r2qkb1r/pbp1p1p1/1pnp1n1p/5p2/4P2P/5NP1/PPPPKPB1/RNBQR3 w kq - 0 8",
//  "r2qkbnr/ppp4p/2np1p2/4p3/3PP3/P2B1N2/1PP2PpP/RNBQ1RK1 b kq - 1 11"
// ]

:eye: Demo (from isepic-chess-ui)

https://ajax333221.github.io/isepic-chess-ui/

:rocket: Features

• Get legal moves
• Lookahead moves that result in checkmate / draw
• Check / checkmate / draw detection
• Pawn promotion options
• PGN import / export
• UCI import / export
• ASCII diagram
• Material difference
• Multiple boards at once
• Number of attackers / defenders on a square
• Navigable move history and helper methods (first, last, previous, undo move, reset, etc.)
• Powerful FEN one-liner operations (Ic.fenApply() and Ic.fenGet())
• Advanced FEN validation
• SAN parsing
• Puzzle mode (:construction: work in progress :construction:)

:book: Documentation

• Examples
• Ic methods
• Board methods
• Board properties
• Square properties
• Move properties

:page_facing_up: Copyright and license

Copyright © 2023 Ajax Isepic (ajax333221)

Licensed under MIT License: http://opensource.org/licenses/mit-license.php