Merge all repeated cells per column using jQuery

mergeTwins.js

/**
 * Find a cell at a given distance below the given cell.
 * @param {jQuery} cell The origin cell below which to find the target.
 * @param {number} steps The number of steps to take.
 * @returns {jQuery} The target cell.
 */
function below(cell, steps) {
	return cell.parent().nextAll().eq(steps - 1).children().eq(cell.index());
	// Get the current row
	// Step down the given amount of rows
	// Go to the index of the origin cell
}

/**
 * Merge all repeated cells in each column.
 * @param {jQuery} table The table to merge cells in.
 * @param {boolean} [includeHeader] Whether to include the header row.
 * @param {boolean} [keepHeight] Whether to include the footer row.
 */
function mergeTwinCells(table, includeHeader = false, keepHeight = true) {
	/**
	 * First row to merge cells in. 
	 * @type {jQuery}
	 */
	let firstRow = table.find('tr').eq(includeHeader + 1);
	/**
	 * Original height of the table.
	 * only set if keepHeight is true.
	 * @type {number|undefined}
	 */
	let height = firstRow.height();
	firstRow.find('td').each(function () {
		for (
			// For each column

			let /** Current cell @type {jQuery} */ thisCell = $(this),
				/** @type {number} */ steps = 1,
				/** @type {jQuery} */ nextCell = below(thisCell, steps);
			nextCell.length; // While there is a next cell

			nextCell = below(thisCell, steps) // Either the current cell or steps are incremented within the loop
		) {
			// Merge twins

			if (thisCell.text() == nextCell.text()) { // If this and next are identical
				// Merge them
				thisCell.attr('rowspan', steps + 1); // rowspan++
				below(thisCell, steps++).attr('hidden', true); // Hide the next cell
			} else {
				// Go to the next cell
				steps = 1; // Reset steps
				thisCell = nextCell; // Increment cell
			}
		}
	});

	if (keepHeight) {
		// Reset the height of the rows with only merged cells
		table.find('tr').each(function () {
			$(this).css('height', height);
		});
	}
}

$(document).ready(function () {
	$('table').each(function () {
		mergeTwinCells($(this));
	});
});