Google Apps Script - Google Sheets - Use the getActiveRangeList() method to get indexes of selected rows

Get indexes of selected rows.gs

function myFunction() {
  const sheet = SpreadsheetApp.getActiveSheet();
  const data = sheet.getDataRange().getValues();
  const selectedRows = getIndexesOfSelectedRows(sheet);
  for (let i = 0; i < data.length; i++) {
    // skip not selected rows
    if (!selectedRows.includes(i + 1)) continue;
    const rowData = data[i];
    console.log(rowData);
    // perform the relevant action: generate a document, send an email,...
  }
}

/**
 * @param {SpreadsheetApp.Sheet} dataSheet
 * 
 * @returns {Array<number>} selectedRows an array of row indexes for all selected rows; row indexing starts with 1.
 */
function getIndexesOfSelectedRows(dataSheet) {
  let selectedRowsIndexes = [];
  // check current selection
  // if specific row(s) are selected, allow user to perform a merge only on those rows
  const rangeList = dataSheet.getActiveRangeList();
  const ranges = rangeList.getRanges();
  for (let i in ranges) {
    const a1Notation = ranges[i].getA1Notation();
    // if range notation doesn't contain ":", it's a single cell, skip it
    if (!a1Notation.includes(":")) continue;
    const tmp = a1Notation.split(":").map(Number);
    // if range notation contains a letter, specific columns are selected, not a whole row, skip it
    if (!Number.isInteger(tmp[0]) || !Number.isInteger(tmp[1])) continue;
    if (tmp[0] == tmp[1]) {
      selectedRowsIndexes.push(tmp[0]);
    }
    else {
      for (let j = tmp[0]; j < tmp[1] + 1; j++) {
        selectedRowsIndexes.push(j);
      }
    }
  }
  return selectedRowsIndexes;
}

/**
 * similar behavior can be tested in Mergo (mail merge) & Publigo (document merge)
 * https://workspace.google.com/marketplace/app/mergo_mail_merge/91302273949?pann=b
 * https://workspace.google.com/marketplace/app/publigo_document_merge/677216675116?pann=b
 */