TypeScript 프로젝트에 싱글톤 패턴 적용

1. 싱글톤 패턴

한 클래스의 객체(인스턴스)가 하나밖에 생성하지 않는 방식을 싱글톤 패턴이라고 한다.

장점은 메모리가 덜 낭비되는 것이라고 하는데 아직 직접 겪어보지는 못했다.

2. 기존 코드

import express, { NextFunction, Request, Response } from "express";
import helmet from "helmet";
import morgan from "morgan";
import authRouter from "./auth/auth.router";
import config from "./config";
import db from "./database";
import rateLimiter from "./middleware/rateLimiter";
import tweetRouter from "./tweet/tweet.router";

const app = express();

app.use(express.json());
app.use(morgan("dev"));
app.use(helmet());
app.use(rateLimiter);

app.use("/auth", authRouter);
app.use("/tweet", tweetRouter);

app.use((req: Request, res: Response, next: NextFunction) => {
  res.status(404).send("NOT FOUND");
});

app.use((err: any, req: Request, res: Response, next: NextFunction) => {
  res.status(500).send(err);
});

db.sync().then(() => {
  app.listen(config.port, () => {
    console.log("Server On...");
  });
});

3. 싱글톤 패턴 적용

import express, { NextFunction, Request, Response } from "express";
import helmet from "helmet";
import morgan from "morgan";
import authRouter from "./auth/auth.router";
import config from "./config";
import db from "./database";
import rateLimiter from "./middleware/rateLimiter";
import tweetRouter from "./tweet/tweet.router";
import cors from "cors";

class Server {
  private app: express.Application;

  constructor() {
    this.app = express();
  }

  // 라우터
  private setRouter() {
    this.app.use("/auth", authRouter);
    this.app.use("/tweet", tweetRouter);
  }

  // 에러 핸들러
  private setErrorHandler() {
    this.app.use((req: Request, res: Response, next: NextFunction) => {
      res.status(404).send("NOT FOUND");
    });

    this.app.use(
      (err: any, req: Request, res: Response, next: NextFunction) => {
        res.status(500).send(err);
      }
    );
  }

  // 미들웨어
  private setMiddleware() {
    this.app.use(express.json());
    if (config.nodeEnv === "production") {
      console.log(`config.nodeEnv === "production"`);

      this.app.use(morgan("combined"));
    } else {
      console.log(`config.nodeEnv === "develop"`);

      this.app.use(morgan("dev"));
    }
    this.app.use(helmet());
    this.app.use(rateLimiter);
    this.app.use(cors());

    this.setRouter();

    this.setErrorHandler();
  }

  // DB 연결 & 서버 실행
  public listen() {
    this.setMiddleware();

    db.sync().then(() => {
      this.app.listen(config.port, () => {
        console.log("Server On...");
      });
    });
  }
}

function init() {
  const server = new Server();

  server.listen();
}

init();