Immutable type safe dependency container for TypeScript

DependencyContainer.ts

class DependencyContainer<T> {
  constructor(
    private factories: Record<string, (self: any) => any> = {},
    private objects: Record<string, any> = {}
  ) {}

  set<K extends keyof T | (string & {}), V>(
    key: K,
    factory: (self: DependencyContainer<T>) => V
  ): DependencyContainer<T & { [P in K]: V }> {
    return new DependencyContainer({ ...this.factories, [key]: factory });
  }

  get<K extends keyof T>(key: K): T[K] {
    let object = this.objects[key as any];
    if (!object) {
      object = this.factories[key as any](this);
      this.objects[key as any] = object;
    }
    return object;
  }
}