Singleton in TypeScript
Singleton is a creational design pattern, which ensures that only one object of its kind exists and provides a single point of access to it for any other code.
Singleton has almost the same pros and cons as global variables. Although they’re super-handy, they break the modularity of your code.
You can’t just use a class that depends on a Singleton in some other context, without carrying over the Singleton to the other context. Most of the time, this limitation comes up during the creation of unit tests.
Complexity:
Popularity:
Usage examples: A lot of developers consider the Singleton pattern an antipattern. That’s why its usage is on the decline in TypeScript code.
Identification: Singleton can be recognized by a static creation method, which returns the same cached object.
Conceptual Example
This example illustrates the structure of the Singleton design pattern and focuses on the following questions:
- What classes does it consist of?
- What roles do these classes play?
- In what way the elements of the pattern are related?
index.ts: Conceptual example
/** * The Singleton class defines an `instance` getter, that lets clients access * the unique singleton instance. */ class Singleton { static #instance: Singleton; /** * The Singleton's constructor should always be private to prevent direct * construction calls with the `new` operator. */ private constructor() { } /** * The static getter that controls access to the singleton instance. * * This implementation allows you to extend the Singleton class while * keeping just one instance of each subclass around. */ public static get instance(): Singleton { if (!Singleton.#instance) { Singleton.#instance = new Singleton(); } return Singleton.#instance; } /** * Finally, any singleton can define some business logic, which can be * executed on its instance. */ public someBusinessLogic() { // ... } } /** * The client code. */ function clientCode() { const s1 = Singleton.instance; const s2 = Singleton.instance; if (s1 === s2) { console.log( 'Singleton works, both variables contain the same instance.' ); } else { console.log('Singleton failed, variables contain different instances.'); } } clientCode(); Output.txt: Execution result
Singleton works, both variables contain the same instance. 
