Convert a Chess Board Diagram into a FEN string in the browser using javascript without any modules

Question

I've seen a post explaining how to do this but in python, but it was done in a python library, so I tried converting it to javascript without a library and this is how it turned out.

function board_to_fen(board)
{
    let result = "";
    for(let y = 0; y < board.length; y++)
    {
        let empty = 0;
        for(let x = 0; x < y.length; x++)
        {
            let c = y[x][0];
            if(c == 'w' || c == 'b') {
                if(empty > 0)
                {
                    result += empty.toString();
                    empty = 0;
                }
                if(c == 'w')
                {
                    result += y[x][1].toUpperCase();
                } else {
                    result += y[x][1].toLowerCase();
                }                
            } else {
                empty += 1;
            }
        }
        if(empty == 0)
        {
            result += empty.toString();
        }
        result += '/';        
    }
    result += ' w KQkq - 0 1';
    return result;
}

let board = [
    ['bk', 'em', 'em', 'em', 'em', 'em', 'em', 'em'],
    ['em', 'bn', 'em', 'wr', 'em', 'wp', 'em', 'em'],
    ['br', 'em', 'bp', 'em', 'em', 'bn', 'wn', 'em'],
    ['em', 'em', 'bp', 'bp', 'bp', 'em', 'wp', 'bp'],
    ['bp', 'bp', 'em', 'bp', 'wn', 'em', 'wp', 'em'],
    ['em', 'em', 'em', 'em', 'em', 'em', 'em', 'em'],
    ['em', 'em', 'em', 'wk', 'em', 'em', 'em', 'em'],
    ['em', 'em', 'em', 'em', 'em', 'em', 'em', 'em'],
];

console.log(board_to_fen(board));

The correct fen for that Chess Board Diagram is "k7/1n1R1P2/r1p2nN1/2ppp1Pp/pp1pN1P1/8/3K4/8 w KQkq - 0" but in the console it prints out "0/0/0/0/0/0/0/0/ w KQkq - 0 1".

Trentium · Accepted Answer · 2020-06-28 21:13:57Z

Just required some minor fixes when referencing the board. Occurrences of y[x] essentially needed to be changed to board[y][x], as y is an index into the board array.

function board_to_fen(board)
{
    let result = "";
    for(let y = 0; y < board.length; y++)
    {
        let empty = 0;
        for(let x = 0; x < board[y].length; x++)
        {
            let c = board[y][x][0];  // Fixed
            if(c == 'w' || c == 'b') {
                if(empty > 0)
                {
                    result += empty.toString();
                    empty = 0;
                }
                if(c == 'w')
                {
                    result += board[y][x][1].toUpperCase();  // Fixed
                } else {
                    result += board[y][x][1].toLowerCase();  // Fixed
                }                
            } else {
                empty += 1;
            }
        }
        if(empty > 0)   // Fixed
        {
            result += empty.toString();
        }
        if(y < board.length - 1)  // Added to eliminate last '/'
        {
          result += '/';
        }
    }
    result += ' w KQkq - 0 1';
    return result;
}

let board = [
    ['bk', 'em', 'em', 'em', 'em', 'em', 'em', 'em'],
    ['em', 'bn', 'em', 'wr', 'em', 'wp', 'em', 'em'],
    ['br', 'em', 'bp', 'em', 'em', 'bn', 'wn', 'em'],
    ['em', 'em', 'bp', 'bp', 'bp', 'em', 'wp', 'bp'],
    ['bp', 'bp', 'em', 'bp', 'wn', 'em', 'wp', 'em'],
    ['em', 'em', 'em', 'em', 'em', 'em', 'em', 'em'],
    ['em', 'em', 'em', 'wk', 'em', 'em', 'em', 'em'],
    ['em', 'em', 'em', 'em', 'em', 'em', 'em', 'em'],
];

console.log(board_to_fen(board));

For those landing here, see also stackoverflow.com/questions/68976802/…

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