how to define my database connection correctly in postgres with nodejs

Question

var config = require('config.json');
var _ = require('lodash');
var jwt = require('jsonwebtoken');
var bcrypt = require('bcryptjs');
var Q = require('q');
var pg= require('pg');
var conString = "postgres://postgres:12345@localhost/alaa";

var service = {};

service.authenticate = authenticate;
service.getById = getById;
service.create = create;
service.update = update;
service.delete = _delete;

module.exports = service;

function authenticate(username, password) {
	    var deferred = Q.defer();
        var conString = "postgres://postgres:12345@localhost/alaa";

    pg(conString, function (err, user) {
        if (err) deferred.reject(err.name + ': ' + err.message);

        if (user && bcrypt.compareSync(password, user.hash)) {
            // authentication successful
            deferred.resolve(jwt.sign({ sub: user._id }, config.secret));
        } else {
            // authentication failed
            deferred.resolve();
        }
    });

    return deferred.promise;
}

function getById(_id) {
    var deferred = Q.defer();

  client.query('SELECT * FROM users WHERE id = $1', [id], function (err, user) {
        if (err) deferred.reject(err.name + ': ' + err.message);

        if (user) {
            // return user (without hashed password)
            deferred.resolve(_.omit(user, 'hash'));
        } else {
            // user not found
            deferred.resolve();
        }
    });

    return deferred.promise;
}

function create(userParam) {
    var deferred = Q.defer();

    // validation
    pg(conString,
        { username: userParam.username },
        function (err, user) {
            if (err) deferred.reject(err.name + ': ' + err.message);

            if (user) {
                // username already exists
                deferred.reject('Username "' + userParam.username + '" is already taken');
            } else {
                createUser();
            }
        });

    function createUser() {
        // set user object to userParam without the cleartext password
        var user = _.omit(userParam, 'password');

        // add hashed password to user object
        user.hash = bcrypt.hashSync(userParam.password, 10);
        var query = 'INSERT INTO users(user, password) VALUES ($1, $2)';
       pg(conString,
            function (err, user,doc) {
                if (err) deferred.reject(err.name + ': ' + err.message);

                deferred.resolve();
            });
    }

    return deferred.promise;
}

function update(_id, userParam) {
    var deferred = Q.defer();

    // validation
  client.query('SELECT * FROM users WHERE id = $1', [id], function (err, user) {
        if (err) deferred.reject(err.name + ': ' + err.message);

        if (user.username !== userParam.username) {
            // username has changed so check if the new username is already taken
            db.users.findOne(
                { username: userParam.username },
                function (err, user) {
                    if (err) deferred.reject(err.name + ': ' + err.message);

                    if (user) {
                        // username already exists
                        deferred.reject('Username "' + req.body.username + '" is already taken')
                    } else {
                        updateUser();
                    }
                });
        } else {
            updateUser();
        }
    });

    function updateUser() {
        // fields to update
        var set = {
            firstName: userParam.firstName,
            lastName: userParam.lastName,
            username: userParam.username,
        };

        // update password if it was entered
        if (userParam.password) {
            set.hash = bcrypt.hashSync(userParam.password, 10);
        }

        pg(conString,
            
            function (err, doc) {
                if (err) deferred.reject(err.name + ': ' + err.message);

                deferred.resolve();
            });
    }

    return deferred.promise;
}

function _delete(_id) {
    var deferred = Q.defer();

    client.query('DELETE FROM users WHERE id = $1', [id],
        function (err) {
            if (err) deferred.reject(err.name + ': ' + err.message);

            deferred.resolve();
        });

    return deferred.promise;
}

and i get this error

so i want to know how to define postgres connection correctly to work with the loginpage and use for loginpage this tutorial

http://jasonwatmore.com/post/2015/12/09/mean-stack-user-registration-and-login-example-tutorial

but the problem with me that is the tutorial with mongodb and i want to make login page working with postgres database