eraseSelected.js

class Game extends Compoent {
...  
  eraseSelected = () => {
    const selectedCell = this.getSelectedCell();
    if (!selectedCell) return;
    this.fillNumber(false);
  }

  fillSelectedWithSolution = () => {
    const { board, solution } = this.state;
    const selectedCell = this.getSelectedCell();
    if (!selectedCell) return;
    const { x, y } = board.get('selected');
    this.fillNumber(solution[x][y]);
  }
...
}