Getting Started with Express

{
  "name": "bookshelf-api",
  "version": "0.1.0",
  "private": true,
  "type": "module",
  "engines": { "node": ">=18" },
  "dependencies": {
    "express": "^5.3.0"
  }
}

// app.js (with "type": "module" in package.json)
import express from 'express';

const app = express();
const port = 3000;

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});

node app.js
curl -i http://localhost:3000/

HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: text/html; charset=utf-8
Content-Length: 12
ETag: W/"c-Lve95gjOVATpfV8EL5X4nxwjKHE"

Hello World!

// index.cjs (or app.js in a project without "type": "module")
const express = require('express');

const app = express();
const port = 3000;

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});

npm install --save-dev typescript @types/express @types/node

// src/app.ts
import express, { type Express, type Request, type Response } from 'express';

const app: Express = express();
const port = 3000;

app.get('/', (req: Request, res: Response) => {
  res.send('Hello World!');
});

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});

{
  "compilerOptions": {
    "target": "esnext",
    "module": "nodenext",
    "rewriteRelativeImportExtensions": true,
    "erasableSyntaxOnly": true,
    "verbatimModuleSyntax": true,
    "noEmit": true,
    "strict": true,
    "skipLibCheck": true
  }
}

node src/app.ts      # Node.js strips the types: no build step (22.18+ or 23.6+)
npx tsc              # type-check only: Node.js does not check types

// app.js
import express from 'express';

const app = express();
const port = Number(process.env.PORT ?? 3000);

const books = [
  { id: 1, title: 'Dune', author: 'Frank Herbert' },
  { id: 2, title: 'Neuromancer', author: 'William Gibson' },
];

app.get('/api/v1/books', (req, res) => {
  res.json(books);
});

app.listen(port, (error) => {
  if (error) {
    throw error;
  }
  console.log(`Bookshelf API listening on http://localhost:${port}`);
});

import express from 'express';

const app = express();
const port = Number(process.env.PORT ?? 3000);

const server = app.listen(port, '0.0.0.0', (error) => {
  if (error) {
    console.error(`Cannot listen on port ${port}: ${error.code}`);
    process.exit(1);
  }
  console.log(`Listening on ${JSON.stringify(server.address())}`);
});

npx express-generator --view=pug --git bookshelf-admin
cd bookshelf-admin
npm install
DEBUG=bookshelf-admin:* npm start

.
├── app.js
├── bin
│   └── www
├── package.json
├── public
│   ├── images
│   ├── javascripts
│   └── stylesheets
│       └── style.css
├── routes
│   ├── index.js
│   └── users.js
└── views
    ├── error.pug
    ├── index.pug
    └── layout.pug

// app.js: the modernised app, exported without listening
import path from 'node:path';
import express from 'express';
import createError from 'http-errors';
import logger from 'morgan';
import cookieParser from 'cookie-parser';
import indexRouter from './routes/index.js';

const app = express();

app.set('views', path.join(import.meta.dirname, 'views'));
app.set('view engine', 'pug');
app.disable('x-powered-by');

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(import.meta.dirname, 'public')));

app.use('/', indexRouter);

app.use((req, res, next) => {
  next(createError(404));
});

app.use((err, req, res, next) => {
  res.status(err.status ?? 500);
  res.render('error', {
    message: err.message,
    error: req.app.get('env') === 'development' ? err : {},
  });
});

export default app;

// server.js: the only file that listens
import app from './app.js';

const port = Number(process.env.PORT ?? 3000);

const server = app.listen(port, (error) => {
  if (error) {
    console.error(`Cannot listen on port ${port}: ${error.code}`);
    process.exit(1);
  }
  console.log(`Listening on ${JSON.stringify(server.address())}`);
});

{
  "scripts": {
    "start": "node server.js",
    "dev": "node --watch --env-file=.env server.js"
  }
}