How I can write this code to work properly in nodejs

I have config.js in my nodejs project

var mysql  = require('mysql');
var db_name = 'node';
var client = mysql.createClient({
  user: 'root',
  password: 'pass',
});
client.query('USE '+db_name);

I have used it as config file for the project. How I can use this code to call a mysql query.

I have this code in user.js

var global = require('./config.js');

this.CheckUserValid = function (login, pass) {
    var sql = "SELECT * FROM `user` WHERE login = ? AND pass= ?";
    global.client.query(sql, [login, pass], function selectResutl(err, results, fields) {
        if (!err) return results;
        else
            throw err;
    });
}

TypeError: Cannot call method 'query' of undefined
    at Object.CheckUserValid (C:\wamp\www\Node\user.js:6:19)

Can someone help me to let me know how I can do this in better way.Actually I am using asp.net mvc in my past so I have tried it. Do someone tell me the better way to write code in nodejs.