Extract and combine first row of CSV files with Google Apps Script

Code.gs

function extractFirstRowCsvWithFilename() {
  const folder = DriveApp.getFolderById("1MBaI_rGJ6t_loANMAvGpDbr2MeHZwxnn");
  const files = folder.getFilesByType(MimeType.CSV);
  let combinedData = [];

  while (files.hasNext()) {
    let file = files.next();
    let filename = file.getName();
    let csvData = Utilities.parseCsv(file.getBlob().getDataAsString());

    // Add the filename to the first column.
    csvData[0].unshift(filename);
    combinedData.push(csvData[0]);
  }
  folder.createFile("CombinedFirstRowWithFilename.csv", combinedData.join("\n"), MimeType.CSV);
}