Applying the Singleton Pattern in TypeScript

The Singleton pattern is one of the most widely known and frequently used design patterns in software development. It is a creational pattern and it ensures that a class has only one instance. Although its conceptual simplicity makes it attractive, its practical usage can have architectural consequences, both in positive and negative way. At the end of the day, nothing is a magic stick, every tool has an area of use.

Historically, the Singleton pattern gained popularity through its use in object-oriented languages such as C#, Java and C++ etc. In the languages managing shared resources like database connections, file systems, or logging mechanisms required a centralized point of access. In more modern environments, particularly in frontend and full-stack TypeScript applications, the pattern still plays a vital role, especially when working with stateful services, application-wide configuration, or platform bridges like browser APIs.

One of the primary advantages of the Singleton pattern is the controlled access to a single instance. This can be valuable when managing global state or coordinating shared dependencies. By encapsulating instantiation logic, the Singleton ensures consistency across the application by reducing the unintended side effects caused by multiple instances. Because the instance is typically created lazily (only when needed), resource allocation remains efficient. Singleton implementations can also help enforce certain constraints in distributed or modular systems where a central authority or coordinator is necessary.

However, there are trade-offs. Singletons, when overused, can become a form of global state—difficult to test, hard to scale, and prone to creating tight coupling between components. This can lead to hidden dependencies that undermine modular design. In multi-threaded environments (less of a concern in TypeScript, but critical in other contexts), Singleton implementations require careful synchronization to avoid race conditions during instantiation. Additionally, mocking or replacing a Singleton for testing purposes often requires workarounds or additional abstraction layers.

Let’s come back to our point and look at how the Singleton pattern can be implemented in TypeScript. The language’s class syntax and module system make it straightforward to define and control instantiation logic.

class Configuration {
  private static instance: Configuration;
  private settings: Record<string, string> = {};

  private constructor() {
    // Simulate loading configuration
    this.settings = {
      apiUrl: 'https://api.example.com',
      env: 'production',
    };
  }

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

  getSetting(key: string): string | undefined {
    return this.settings[key];
  }
}

In this example, the Configuration class encapsulates a key-value store that might represent application-wide configuration data. The constructor is marked private to prevent direct instantiation. Instead, access to the single instance is managed through the static getInstance() method. This ensures that throughout the application lifecycle, all consumers of Configuration refer to the same shared instance.

Using this pattern is straightforward:

const config = Configuration.getInstance();
console.log(config.getSetting('apiUrl'));

This pattern becomes especially powerful when paired with dependency injection or used in combination with other patterns such as the Factory or Service Locator. However, it’s important to remain cautious. Just because something can be a Singleton doesn’t mean it should be. Introducing single points of state or logic into a large-scale TypeScript application may simplify some interactions while complicating others. Especially when dealing with asynchronous code, test suites, or dynamic runtime environments like serverless functions.

In conclusion, the Singleton pattern is a relevant and effective tool for solving specific architectural problems in TypeScript projects. Its strength lies in providing controlled, centralized access to shared resources. However, that strength can also become a liability if not used with care. As with any pattern, context is everything. When applied with deliberate intent and thoughtful design, Singletons can contribute to clean, maintainable, and scalable software systems.

Suleyman Cabir Ataman, PhD

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