Typescript/Node Dependency Injector (DI) - Koa server sample

main.di.ts

import * as Koa from "koa";

let koaInstance: Koa;
class AppInjector {
  static injectApp() {
    if (!koaInstance) {
      koaInstance = new Koa();

      koaInstance.use(async (ctx) => {
        ctx.body = "Hello World";
      });
    }
    return koaInstance;
  }
  static injectPort() {
    return 3000;
  }
}

class Server {
  private _app: Koa;
  private _port: number;

  constructor() {
    this._app = AppInjector.injectApp();
    this._port = AppInjector.injectPort();
  }

  start() {
    this._app.listen(this._port);
  }
}

const main = () => {
  const server = new Server();
  server.start();
};

main();

main.ts

import * as Koa from "koa";

class Server {
  private _app: Koa;
  private _port: number;

  constructor(port: number) {
    this._app = new Koa();
    this._port = port;

    this._app.use(async (ctx) => {
      ctx.body = "Hello World";
    });
  }

  start() {
    this._app.listen(this._port);
  }
}

const main = () => {
  const server = new Server(3000);
  server.start();
};

main();