use Array.map instead of crap

original.jsx

  render() {
    return (
      <div>
        <div className="board-row">
          {this.renderSquare(0)}
          {this.renderSquare(1)}
          {this.renderSquare(2)}
        </div>
        <div className="board-row">
          {this.renderSquare(3)}
          {this.renderSquare(4)}
          {this.renderSquare(5)}
        </div>
        <div className="board-row">
          {this.renderSquare(6)}
          {this.renderSquare(7)}
          {this.renderSquare(8)}
        </div>
      </div>
    );
  }

using_map.jsx

  render() {
    return (
      <div>
        {[0, 3, 6].map(j => (
          <div key={j} className="board-row">
            {[j, j + 1, j + 2].map(
                i => this.renderSquare(i)
            )}
          </div>
        ))}
      </div>
    );
  }