This code uses the Gmail JavaScript API to search the inbox of the authenticated user (userId = me) for email threads that match the specified query. You need to create a new project in Google developer console with the Gmail API enabled.

The scope can be https://www.googleapis.com/auth/gmail.readonly since this Gmail app requires only read only access to the user’s mailbox.

var threads = function listGmailThreads(userId, query, callback) {
  var getPageOfThreads = function (request, result) {
    request.execute(function (resp) {
      result = result.concat(resp.threads);
      var nextPageToken = resp.nextPageToken;
      if (nextPageToken) {
        request = gapi.client.gmail.users.threads.list({
          userId: userId,
          q: query,
          pageToken: nextPageToken,
        });
        getPageOfThreads(request, result);
      } else {
        callback(result);
      }
    });
  };
  var request = gapi.client.gmail.users.threads.list({
    userId: userId,
    q: query,
  });
  getPageOfThreads(request, []);
};