table2excel/src/helpers/table-to-data.js

convert and download html tables to a xlsx-file that can be opened in Microsoft Excel

/**
 * Calculates the cells and its rowspans and colspans of a table.
 *
 * `cells` is a 2-d array containing the HTMLTableCellElement cells.
 * Rowspans and Colspans are indicated as `null` values.
 *
 * Rowspans and Colspans are also saved in `ranges`.
 * An element contains the start and end position of a rowspan or
 * colspan like { s: { r: 1, c: 1 }, e: { r:1, c: 4} }.
 *
 * @param {HTMLTableElment} table - The table.
 * @returns { { cells: Array, ranges: Array } } - The table object.
 */
export default function tableToData(table) {
  const cells = [];
  const ranges = [];

  // iterate over all rows
  Array.from(table.querySelectorAll('tr')).forEach((row, rowIndex) => {
    cells.push([]);

    // iterate over all cells in the row
    Array.from(row.querySelectorAll('td, th'))
      .filter(cell => cell.style.display !== 'none')
      .forEach(cell => {
        ranges.forEach(range => {
          if (  // we are in a rowspan (already saved in ranges)
            rowIndex >= range.s.r &&
            rowIndex <= range.e.r &&
            cells[rowIndex].length >= range.s.c &&
            cells[rowIndex].length <= range.e.c
          ) {
            // ... fill the cells with empty values
            for (let i = range.s.c; i < range.e.c; i++) {
              cells[rowIndex].push(null);
            }
          }
        });

        // detect rowspan or colspan
        const colspan = parseInt(cell.colSpan, 10) || 1;
        const rowspan = parseInt(cell.rowSpan, 10) || 1;

        if (rowspan > 1 || colspan > 1) {
          ranges.push({
            s: {
              r: rowIndex,
              c: cells[rowIndex].length,
            },
            e: {
              r: rowIndex + rowspan - 1,
              c: cells[rowIndex].length + colspan - 1,
            },
          });
        }

        cells[rowIndex].push(cell);

        // if we are in a following colspan ...
        if (colspan > 1) {
          for (let i = 1; i < colspan; i++) cells[rowIndex].push(null);
        }
      });
  });

  return { cells, ranges };
}