なんてことはありません

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  password: 'pass',
  database: 'db_name'
});

connection.query(`INSERT INTO user_table (name, mail, pass) VALUES ('${user_name}', '${user_name}', '${user_name}');`, function (err, result, fields) {
  if (err) throw err;
  });