Classes and Object-Oriented TypeScriptLesson 5.3

Static members and singleton pattern in TypeScript

static properties, static methods, class-level vs instance-level, static blocks, singleton pattern implementation

Static members

Static members belong to the class, not to instances:

class MathUtils {
  static readonly PI = 3.14159;

  static circleArea(radius: number): number {
    return MathUtils.PI * radius ** 2;
  }
}

MathUtils.circleArea(5); // no instance needed

Singleton pattern

Use a private constructor and a static instance to enforce a single object:

class Config {
  private static instance: Config | null = null;
  private data: Record = {};

  private constructor() {}

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

  set(key: string, value: string): void { this.data[key] = value; }
  get(key: string): string | undefined   { return this.data[key]; }
}

const cfg = Config.getInstance();
cfg.set("env", "production");