try{
    var db = connect('admin');
    if(db.system.users.find({'user':'root'}).count() == 0){
        print('Ready to addUser...');
        db.createUser({ user: 'root', pwd: 'xmjkzl', roles: [ { role:"userAdminAnyDatabase", db: "admin" } ,{ role:"readWriteAnyDatabase", db: "admin" }] });
    }else{
        print('Already exist user.')
    }
}catch(err){
    print('Error occured:' + err);
}