text: function chessboard(n) {
      let html = '<div class="chessboard">\n';
      for (let row = 0; row < n; row ++) {
          html += '<div>\n';
          let color = (row % 2 == 0) ? 'black': 'white';
          for (let col = 0; col < n; col ++){
              html += ` <span class="${color}"></span>\n`;
              color = (color == 'white') ? 'black':'white';
          }
          html += '</div>\n';
      }
          return html + '</div>'
  }