request.js

function getUsers() {
    var req = {
      method: 'GET',
      url: 'http://localhost:3000/api/getUsers',
      headers: {
        'app-key': 'CopyXwPp9xazJ0ku5CZnlmgAx2Dld8SHkAeT',
        token: $cookies.get('token')
      }
    };
    $http(req).then(function(res) {
      console.log('here: ', res.data.data);
      $scope.users = res.data.data;
    }, function(res) {
      console.log('error', res);
    });
  };

returnInsideNestPromise.js

function getUsers(req, res) {
  return Role
    .findOne({name: 'admin'})
    .then(role => {
      User
        .find()
        .populate({
          path: 'roleId nationId',
          select: '-__v -createdAt -updatedAt -role'
        })
        .where('roleId')
        .nin([role._id])
        .select('-__v -password -createdAt -updatedAt')
        .then(users => {
          return res.json({
            isSuccess: true,
            data: users
          });
        })
        .catch(err => {
          return res.json({
            isSuccess: false,
            errorText: err.message
          });
        });
  })
}

function getUsers(req, res) {
    Role
        .findOne({
            name: 'admin'
        })
        .then(role => {
            return User
                .find()
                .populate({
                    path: 'roleId nationId',
                    select: '-__v -createdAt -updatedAt -role'
                })
                .where('roleId')
                .nin([role._id])
                .select('-__v -password -createdAt -updatedAt')
                .then(users => {
                    return res.json({
                        isSuccess: true,
                        data: users
                    });
                });
        })
        .catch(err => {
            return res.json({
                isSuccess: false,
                errorText: err.message
            });
        });
}