selectCell.js

class Game extends Compoent {
...  
  getSelectedCell() {
    const { board } = this.state;
    const selected = board.get('selected');
    return selected && board.get('puzzle').getIn([selected.x, selected.y]);
  }

  selectCell = (x, y) => {
    let { board } = this.state
    board = board.set('selected', { x, y })
    this.setState({ selected: { x, y }, board})
  }
...
}