Observer & Singleton Patterns

Which code represents a proper Singleton Pattern implementation in modern JavaScript?

class Configuration {
  constructor() {
    if (Configuration.instance) {
      return Configuration.instance;
    }
    
    this.config = {};
    Configuration.instance = this;
  }

  static getInstance() {
    if (!Configuration.instance) {
      Configuration.instance = new Configuration();
    }
    return Configuration.instance;
  }

  set(key, value) {
    this.config[key] = value;
  }

  get(key) {
    return this.config[key];
  }
}

The constructor should be private
getInstance should be an instance method
The implementation correctly ensures single instance creation
This code demonstrates a proper Singleton implementation in JavaScript that: 1) Uses the constructor to check for existing instances, 2) Provides a static getInstance method for access, 3) Maintains a single instance through a static property, and 4) Includes methods to interact with the singleton's data. While JavaScript doesn't support private constructors, this pattern effectively ensures only one instance exists.
The config object should be static

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