Recursively iterate over Google Drive files and folders in Google Apps Script with continuation support

ScanFolder.gs

function scanFolder(folder, stopTime, callback) {
  let ct = null;
  const properties = PropertiesService.getScriptProperties();

  // Iterate files
  ct = properties.getProperty('iter:' + folder.getId() + ':files')
  let files = folder.getFiles();
  if(ct) files = DriveApp.continueFileIterator(ct);
  while(files.hasNext()) {
    const file = files.next();
    callback('file', file);
    if(files.hasNext()) {
      ct = files.getContinuationToken();
      properties.setProperty('iter:' + folder.getId() + ':files', ct);
    }
    if(Date.now() > stopTime) return;
  }

  // Iterate folders
  ct = properties.getProperty('iter:' + folder.getId() + ':folders');
  let folders = folder.getFolders();
  if(ct) folders = DriveApp.continueFolderIterator(ct);
  while(folders.hasNext()) {
    const _folder = folders.next();
    callback('folder', _folder);
    scanFolder(_folder, stopTime, callback);
    if(folders.hasNext()) {
      ct = folders.getContinuationToken();
      properties.setProperty('iter:' + folder.getId() + ':folders', ct)
    }
    if(Date.now() > stopTime) return;
  }
}

// Sample usage
function cb(type, f) {
  console.log(type, f.getName())
}

function test() {
  scanFolder(DriveApp.getFolderById(''), Date.now() + 300000, cb);
}