javascript - Nodejs + express promisse

I'm having difficulty understanding how works promise, I tried to create promise with express, to query on mysql and get results. I read that it is not cool to make this synchronous. I'm trying to make a little game, this route is for the registration.

var lang = require('../lang.js');
var config  =  require('../config.js');
var fieldValidator = require('../libs/field_validator');
var microtime = require('microtime');
var crypto = require('crypto');
//Presets
var lang = new lang();

var rlang = lang.returnMessage;
var fieldValidator = new fieldValidator();
var moment = require('moment');

module.exports = function(app, my){
    //Primeiro os registros
    /// Account Register
    ////
    var check_username = function(username){
        return new Promise(function(resolve, reject) {

            my.query('SELECT username FROM 4h_users WHERE ?', username, function (error, result, fields) {
                if (error) {
                    reject({"status": "error", "code":10 ,"message": rlang(lang, 10)});
                }else{
                    if(result.lenght > 0){
                        reject({"status": "error", "code":10 ,"message": rlang(lang, 10)});
                    }else{
                        resolve(true);
                    }
                };

            });
        });
    }
    check_username().then(function(id_user) {
      console.log(value);
    }, function(reason) {
      res.
    });



    app.post('/api/usuario/registrar', function(req, res){
        if(!req.body.lang){
            return res.send({"status": "error", "code":1 ,"message": 'Blank Language'});
        }else{
            var lang = req.body.lang;
        }
        if(!req.body.recode){
            return res.send({"status": "error", "code":4 ,"message": rlang(lang, 4)});
        }else if(!req.body.username){
            return res.send({"status": "error", "code":1 ,"message": rlang(lang, 1)});

        }else if(!req.body.password){
            return res.send({"status": "error", "code":3 ,"message": rlang(lang, 3)});
        }else if(!req.body.email){
            return res.send({"status": "error", "code":5 ,"message": rlang(lang, 5)});
        }else if(req.body.reemail != req.body.email){
            return res.send({"status": "error", "code":6 ,"message": rlang(lang, 6)});
        }

        my.query('SELECT email FROM 4h_users WHERE ?', req.body.email, function (error, result, fields) {
            if (error) {

                return res.send({"status": "error", "code":10 ,"message": rlang(lang, 10)});
            }else{
                return res.send({"status": "error", "code":13 ,"message": rlang(lang, 13)});
            };
        });

        if(!fieldValidator.username.isValid(req.body.username)){
           return res.send({"status": "error", "code":9 ,"message": rlang(lang, 9)});
        }else if(!fieldValidator.email.isValid(req.body.email)){
           return res.send({"status": "error", "code":7 ,"message": rlang(lang, 7)});

        }else if(!fieldValidator.password.isValid(req.body.password)){
           return res.send({"status": "error", "code":8 ,"message": rlang(lang, 8)});
        }

        var ip = generate_ip();
        var salt = crypto.createHash('sha256').update(microtime.now()+req.body.username).digest("hex");
        var password = crypto.createHash('sha512').update(salt+req.body.password).digest("hex");

        var user = {
            username: req.body.username,

            email: req.body.email,
            password: password,
            salt: salt,
            token_expiration: microtime.now(),
            money: config.default_bonus.money,
            hcoins: config.default_bonus.hcoins,
            register_date: moment().format('YYYY-MM-DD HH:mm:ss'),
            token: crypto.createHash('sha256').update(microtime.now()+req.body.username).digest("hex"),
            token_expiration: microtime.now()+config.expiration.login,
            offline_mode_expiration: 0

        };

        //Check if machine ip exists and generate another one
        check_ip_status(my, ip);

        // Time to mysql

        //Add new user to mysql
        my.query('INSERT INTO 4h_users SET ?', user, function (error, result, fields) {
            if (error) {

                console.log(error);
                return res.send({"status": "error", "code":10 ,"message": rlang(lang, 10)});
            }else{
                var machine = {
                    ip: ip,
                    id_user: result.insertId
                };
                //Add new machine to mysql
                my.query('INSERT INTO 4h_machines SET ?', machine, function (error, result, fields) {
                    if (error) {

                        console.log(error);
                        return res.send({"status": "error", "code":10 ,"message": rlang(lang, 10)});
                    }else{
                        return res.send({"status": "success", "code":11 ,"message": rlang(lang, 11)});
                    };
                });
            };
        });
    });
}



function generate_ip(){
    return (Math.floor(Math.random() * 254) + 1) + "." + (Math.floor(Math.random() * 254) + 1) + "." + (Math.floor(Math.random() * 254) + 1) + "." + (Math.floor(Math.random() * 254) + 1);
}
function check_ip_status(my, ip){
    my.query('SELECT ip FROM 4h_machines WHERE ?', ip, function (error, result, fields) {
        if (error) {
            return res.send({"status": "error", "code":10 ,"message": rlang(lang, 10)});
        }else{

            if(result.lenght > 0){
                ip = generate_ip();
                check_ip_status(ip);
            }
        };

    });
}
//id_user, username, salt, password, email, avatar_url, 4h_coins, money, last_login, register_date, token, token_expiration, reputation, actions, email_verify, modo_offline_expiration

and if you have another tips for this code please tell me, i'm learning and any help be very useful to me
thanks