Factory Functions & Singleton Pattern

Which design pattern does this code implement?

const Database = (() => {
  let instance;
  
  function createInstance() {
    const object = new Object({
      data: [],
      add(item) {
        this.data.push(item);
      },
      remove(index) {
        this.data.splice(index, 1);
      }
    });
    return object;
  }
  
  return {
    getInstance: () => {
      if (!instance) {
        instance = createInstance();
      }
      return instance;
    }
  };
})();

Factory pattern
Singleton pattern
This code implements the Singleton pattern: 1) It ensures only one instance of Database exists throughout the application, 2) It uses an IIFE (Immediately Invoked Function Expression) to create a closure for the instance, 3) The getInstance method checks if an instance exists before creating a new one, 4) The actual instance is private and cannot be directly accessed, 5) This pattern is useful for resources that should be shared across the application, 6) Common use cases include configuration managers, connection pools, and caches.
Observer pattern
Module pattern

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