Factory Functions & Singleton Pattern

What type of singleton pattern is implemented here?

// DatabaseConnection.js
let instance = null;

export default {
  getInstance() {
    if (instance === null) {
      instance = {
        connect() { /* connection logic */ },
        query(sql) { /* query logic */ }
      };
    }
    return instance;
  }
};

Class-based singleton
Module-based singleton
This implements a module-based singleton pattern: 1) It leverages the module system to create a singleton, 2) The instance is maintained in module scope, which persists throughout the application, 3) It exports a factory method that manages the singleton instance, 4) Each import of the module references the same singleton instance, 5) This approach works well with ES modules and provides clean dependency management, 6) It's a modern approach to singletons that fits well with JavaScript's module system.
IIFE singleton
Prototype-based singleton

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