How to Create a Memento Database Using JavaScript Lists?

A memento database is a system for storing snapshots of the state of an application at different points in time. Here’s an example of how you could create a simple memento database using JavaScript lists:

class Memento {
  constructor(state) {
    this.state = state;
  }
}

class CareTaker {
  constructor() {
    this.mementos = [];
  }

  addMemento(memento) {
    this.mementos.push(memento);
  }

  getMemento(index) {
    return this.mementos[index];
  }
}

class Originator {
  constructor() {
    this.state = '';
  }

  setState(state) {
    this.state = state;
  }

  createMemento() {
    return new Memento(this.state);
  }

  restoreMemento(memento) {
    this.state = memento.state;
  }
}

// Create a new originator and caretaker
let originator = new Originator();
let careTaker = new CareTaker();

// Update the state of the originator
originator.setState('State 1');

// Store a memento of the state in the caretaker
careTaker.addMemento(originator.createMemento());

// Update the state of the originator again
originator.setState('State 2');

// Store another memento of the state in the caretaker
careTaker.addMemento(originator.createMemento());

// Restore the first state stored in the caretaker
originator.restoreMemento(careTaker.getMemento(0));

// Log the current state of the originator
console.log(originator.state); // State 1

In this example, we have three classes: Memento, CareTaker, and Originator. The Memento class stores the state of the application, the CareTaker class stores all the mementos, and the Originator class is responsible for creating mementos and restoring the state of the application from a memento.

The Originator class has a method createMemento that creates a new Memento object and stores the current state of the application. The CareTaker class has a method addMemento that adds a memento to its list of mementos, and a method getMemento that retrieves a memento from the list.

The Originator class also has a method restoreMemento that restores the state of the application from a memento. You can create an instance of the Originator class and an instance of the CareTaker class, and use them to store and retrieve mementos of the state of the application.