Simple JavaScript Connect four

connect-4.js

function pubSubRegistry(){
    const subscriptions = [];
    
    return {
        publish: function publish(event) {
            subscriptions.forEach(function(subscription) {
                subscription(event);
            });
        },
        subscribe: function subscribe(fn){
            subscriptions.push(fn);
        },
        unsubscribe: function unsubscribe(fn){
            subscriptions.splice(subscriptions.indexOf(fn), 1);
        },
    };
}

const eventRegistry = pubSubRegistry();

type Board = string[][];    

const board: Board = Array(6).fill(Array(7).fill('.'));

type Move = { vector: [number, number], piece: string, board: Board };

type UpdatedBoardEvent = Board;

function nextMove(move: Move): Board {
    const updatedBoard = move.board.map((row, rowIndex) => {
        return row.map((cell, columnIndex) => {
            if (rowIndex === move.vector[0] && columnIndex === move.vector[1]){
                return move.piece;
            }
            return cell;
        });
    }

    return updatedBoard;
}


eventRegistry.subscribe((updateBoard) => {
    setBoardState(updateBoard);
    console.log(updateBoard.map(r => r.join('')).join('\n'));
});


let boardState = board;
const getBoardState = (): Board => boardState;
const setBoardState = (newBoardState): void => boardState = newBoardState

const m = (p, x, y) => {
    eventRegistry.publish(nextMove({
        vector: [x, y],
        piece: p,
        board: getBoardState()      
    }));
}

m('x', 5, 0);
m('o', 5, 1);

m('x', 4, 0);
m('o', 5, 2);

m('x', 4, 1);
m('o', 5, 3);

m('x', 5, 4);
m('o', 5, 1);

m('x', 5, 3);
m('o', 3, 1);