var Connection = require('tedious').Connection;
var config = {
    userName: 'my_user_name',
    password: 'my_password',
    server: 'server_to_access',
    database: 'database_in_SQL_Server_Management_Studio'
};
var connection = new Connection(config);
connection.on('connect', function(err) {
    console.log("Connected");
});

var Connection = require('tedious').Connection;
var Request = require('tedious').Request;



var config = {
    userName: 'my_user_name',
    password: 'my_password',
    server: 'server_to_access',
    database: 'database_in_SQL_Server_Management_Studio'
};
var connection = new Connection(config);
connection.on('connect', function(err) {
    console.log("Connected");
    executeStatement();
});

function executeStatement() {
    request = new Request("SELECT * FROM Employees", function(err, rowCount) {
      if (err) {
        console.log(err);
      } else {
        console.log(rowCount + ' rows');
      }
    });

    request.on('row', function(columns) {
      columns.forEach(function(column) {
        console.log(column.value);
      });
    });
    connection.execSql(request);
}

C:Usersnameattempt>node test.js
Connected
{ [RequestError: Requests can only be made in the LoggedIn state, not the Connec
ting state]
  message: 'Requests can only be made in the LoggedIn state, not the Connecting
state',
  code: 'EINVALIDSTATE' }

C:Usersnameattempt>

connection.on('connect', (err)=>{ RequestWrapper.next(err); });

const queue = [];

class RequestWrapper(){
    constructor(sql){ this.sql = sql; }
    static next(err){
        const next = queue.shift();
        if(next) next(err);
    }
    queue(args){
        return new Promise((ok, fail)=>{
            queue.push((err)=>{
                if(err) fail(err); else ok(this.request(args));
            })
        })
    }
    request(args){
        if(!connection) return Promise.reject(new Error(`connection required`));
        if(!connection.loggedIn || connection.state.name !== 'LoggedIn') return this.queue(args);

        return new Promise((ok, fail)=>{
            try{
                const request = new tedious.Request(this.sql, (err, count, rows)=>{

                    RequestWrapper.next();

                    if(err) return fail(err);
                    ok(rows);
                });
                ...add params here...
                connection.execSql(request);
            }catch(err){
                RequestWrapper.next();
                fail(err);
            }
        });
    }
};