Create a file src/server.ts:

import express from "express";
import cors from "cors";
import morgan from "morgan";

const app = express();

app.use(cors());
app.use(morgan("dev"));
app.use(express.json());

app.get("/", async (req, res) => {
  res.json({ message: "hello!" });
});

const { PORT } = process.env;
app.listen(PORT, () => {
  console.log(`Forum API listening on port ${PORT}`);
});

Select it as the "main" file in package.json:

{
  // ...
  "main": "src/server.ts"
  // ...
}

Add the PORT variable to the .env file. (We will assume 8888 here.)

Run the server with

bun run src/server.ts

and check that it works.

Change to another terminal (install httpie if you don't have it), and run:

http GET localhost:8888/

You should get something like:

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Length: 20
Content-Type: application/json; charset=utf-8
Date: Wed, 24 Apr 2024 17:51:01 GMT
ETag: W/"14-li7HDh+tAWW33cIYjDrXLcX526M"
X-Powered-By: Express

{
    "message": "hello!"
}

Create "scripts" in package.json to launch the server in development and production:

{
  "scripts": {
    "dev": "bun --hot src/server.ts",
    "start": "NODE_ENV=production bun src/server.ts"
  }
}

Start the server with bun run dev and check that if you change server.ts the server reloads.