// Find user if they exist, otherwise return user with first_name 'Nobody'
var user = new GlideQuery('sys_user')
    .where('last_name', 'Luddy')
    .selectOne('first_name')
    .orElse({ first_name: 'Nobody' });

// Find user, otherwise throw an Error that the user couldn't be found
var user = new GlideQuery('sys_user')
    .where('last_name', 'Luddy')
    .selectOne('first_name')
    .get(); // this method can throw if no record is found

// Does a given user exist? Assign boolean to userExists
var userExists = new GlideQuery('sys_user')
   .where('last_name', 'Luddy')
    .selectOne('first_name')
    .isPresent();