for.js

exports.get = function(req, res){
  User.find(null, 'email -_id', function(err, users) {

    if (err) return res.json(500, err);

    var retobj = {};
    var keys = Object.keys(users);
    var i = keys.length;

    while (i--) retobj[i] = users[keys[i]] && users[keys[i]].email;

    res.json(retobj);

  });
};