buildMap.js

const buildMap = (bombPositions) => {
    let positions = Array.from({length: 10}, (value, x) => {
        return Array.from({length: 10}, (value, y) => {
            return {
                position: {x, y},
                value: (isPositionBomb(bombPositions, {x, y})
                ? 'B'
                : getNeighborBombPositions(bombPositions, {x, y}).length
            ),
                visibility: 'hidden' // visible, marked
            };
        });
    });

    return positions;
};

constructor.js

class Board extends Component {

    constructor(props) {

        super(props);

        this.bombPositions = buildBombPositions();

        this.state = {
            boardMap: buildMap(this.bombPositions),
            gameStatus: 'playing' //won, lost
        };

    }
}

leftclick.js

onSquareLeftClick = (position) => {

        this.setState((prevState) => {
            prevState.boardMap[position.x][position.y].visibility = 'visible';

            return {
                boardMap: prevState.boardMap
            }

        };
    };