How to prevent grouping by subject or date when using getThreads() from a label name in Gmail using App-Script?

Issue:

• Currently, It seems it is not possible to get the email messages labeled with a specific label. Only the containing threads labeled with a label is retrievable through Apps script built in libraries.

Solution:

• Use Advanced Gmail service to connect to the Gmail api directly.

• The following snippet gets all messages ids labeled with label name test. You may then use GmailApp.getMessageById to transform the message id array to GmailMessages

Snippet:

function getLabelledMessages(labelName = 'test') {
  const labelIds = Gmail.Users.Labels.list('me').labels.find(
    labelObj => labelObj.name === labelName
  ).id;
  let messagesList, pageToken;
  do {
    messagesList = Gmail.Users.Messages.list('me', {
      labelIds,
      pageToken,
      maxResults: 100,
    });
    const messages = messagesList.messages;
    if (messages) console.log(JSON.stringify(messages));
  } while ((pageToken = messagesList.nextPageToken) !== undefined);
}