Chess and/or Chess960 board structure with useful methods. Somewhat derived from Nibbler, but also somewhat new and improved. Everything useful is in board.js, other files are just for testing.

Surely fast enough for GUI use, though you likely don't want to build an engine around it.

Usage notes:

• Get a board with load_fen()
• Get new boards with board.move() - this has no legality checks!
• So, check moves for illegality first with board.illegal()
• Moves are expected to be in UCI format, e.g. e2e4 and e7e8q etc, except:
• Castling moves are always king-to-rook e.g. e1h1 (which is Chess960 format)
• Given a move which might be the wrong format, pass it through board.c960_castling_converter() first
• All legal moves for a board can be found with board.movegen()
• Various other useful methods exist, for PGN parsing, end of game detection, etc

Example:

const {load_fen} = require("./board");

let foo = load_fen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");

// Obtain a move from some source, e.g. engine / user input.

let move = "e2e4";
move = foo.c960_castling_converter(move);    // Always OK and wise to do this.

if (!foo.illegal(move)) {                    // Note: returns a string (reason for illegality or "")
    foo = foo.move(move);
}

console.log(foo.graphic());