Cache manager singleton

class ApplicationConfig {
  private static instance: ApplicationConfig | undefined;

  private readonly values = new Map<string, string>();

  private constructor() {
    this.values.set("region", "us-east-1");
  }

  static getInstance(): ApplicationConfig {
    if (!ApplicationConfig.instance) {
      ApplicationConfig.instance = new ApplicationConfig();
    }

    return ApplicationConfig.instance;
  }

  get(key: string): string | undefined {
    return this.values.get(key);
  }

  set(key: string, value: string) {
    this.values.set(key, value);
  }
}

const configA = ApplicationConfig.getInstance();
const configB = ApplicationConfig.getInstance();

configA.set("feature.checkoutV2", "enabled");

console.log(configA === configB); // true
console.log(configB.get("feature.checkoutV2")); // enabled