【GAS】別のフォルダを指定する様々な方法

var folderName = "フォルダ名";
var parentFolder = DriveApp.getFolderById("親フォルダのID");
var folder = parentFolder.getFoldersByName(folderName).next();

var folderId = "フォルダID";
var folder = DriveApp.getFolderById(folderId);

var folderPath = "/フォルダ1/フォルダ2/フォルダ3";
var folders = folderPath.split("/");
var folder = DriveApp.getRootFolder();
for (var i = 0; i < folders.length; i++) {
  if (folders[i] !== "") {
    var subFolders = folder.getFoldersByName(folders[i]);
    if (subFolders.hasNext()) {
      folder = subFolders.next();
    } else {
      folder = null;
      break;
    }
  }
}