A simple implementation of Dependency Injection in Angular

Dependency-Injection.ts

class UserService {
  sayHi() {
    console.log('hi');
  }
}

class Component {
  constructor(private user: UserService) {}
}

class Injector {
  private _container = new Map();

  constructor(private _providers: any[] = []) {
    this._providers.forEach((service) =>
      this._container.set(service, new service())
    );
  }

  get(service: any) {
    const serviceInstance = this._container.get(service);
    if (!serviceInstance) {
      throw Error('No Provider found');
    }
    return serviceInstance;
  }
}

const injector = new Injector([UserService]);

const component = new Component(injector.get(UserService));

component.user.sayHi();