copy_folder.gs

function entry() {
  Logger.clear();
  backup('the folder you want to copy');
}

function backup(name) {
  var sourceFolder = name;
  var targetFolder = name + '-bak';

  var source = DriveApp.getFoldersByName(sourceFolder);
  if (source.hasNext()) {
    var target = DriveApp.getFoldersByName(targetFolder);
    if (target.hasNext()) {
        target = target.next();
    }
    else {
      target = DriveApp.createFolder(targetFolder);
    }
    copyFolder(source.next(), target);
  }
}

function copyFolder(source, target) {

  var folders = source.getFolders();
  var files   = source.getFiles();

  while (folders.hasNext()) {
    var folder = folders.next();
    var folderName = folder.getName();
    var log = folderName;
    var targetFolder = target.getFoldersByName(folderName);
    if (targetFolder.hasNext()) {
      targetFolder = targetFolder.next();
    }
    else {
      targetFolder = target.createFolder(folderName);
      log = '### FOLDER MAKE COPY ### ' + log;
      Logger.log(log);
    }
    copyFolder(folder, targetFolder);
  }

  while (files.hasNext()) {
    var file = files.next();
    var fileName = file.getName();
    var log = fileName;
    if (!target.getFilesByName(fileName).hasNext()) {
      file.makeCopy(fileName, target);
      log = '### FILE MAKE COPY ### ' + log;
      Logger.log(log);
    }
  }
}