TemplateMethodPattern.js

class Datastore {
  constructor() {
    if (this.constructor.name === 'Datastore') {
      throw new Error('datastore is abstract and need to be implemented');
    }
  }
  
  connect() {
    throw new Error('method not implemented');
  }
  
  query(query) {
    throw new Error('method not implemented');
  }
  
  disconnect() {
    throw new Error('method not implemented');
  }
  
  process(query){
    this.connect();
    const result = this.query(query);
    this.disconnect();
    return result;
  }
}
 
class MySQLDatastore extends Datastore {
  connect() {
    console.log('mysql connect step');
  }
  
  query(query) {
    console.log(`mysql execute query: ${query}`);
    return ['some data'];
  }
  
  disconnect() {
    console.log('mysql disconnect step');
  }
}
 
class PostgreSQLDatastore extends Datastore {
  connect() {
    console.log('postgresql connect step');
  }
  
  query(query) {
    console.log(`postgresql execute query: ${query}`);
    return ['some data'];
  }
  
  disconnect() {
    console.log('postgresql disconnect step');
  }
}
 
const mySQLDatastore = new MySQLDatastore();
const postgreSQLDatastore = new PostgreSQLDatastore();
 
mySQLDatastore.process('SELECT * FROM users');
postgreSQLDatastore.process('SELECT * FROM users');