$devvkit learn --librarie express.js-guide

Express.js Guide

[nodejs][http][server][api]

JavaScript / TypeScript

Install

npm install express
npm install -D @types/express

Express is the most popular Node.js web framework and the foundation for NestJS, Next.js API routes, and more.

The middleware pattern is its killer feature. Every request passes through a pipeline of functions that can inspect, modify, or short-circuit it.

Express 5 introduces async error handling and improved path matching.

Setup

Basic server· Create a server.

import express from 'express';
const app = express();
app.listen(3000, () => console.log('running'));

Routing

GET route· Handle GET requests.

app.get('/users', (req, res) => { res.json({ users: [] }); });

Route params· Capture dynamic segments.

app.get('/users/:id', (req, res) => res.json({ id: req.params.id }));

Query params· Access query string.

app.get('/search', (req, res) => res.json({ q: req.query.q }));

Middleware

JSON body parser· Parse JSON bodies.

app.use(express.json());

CORS· Enable CORS.

import cors from 'cors';
app.use(cors());

Custom middleware· Log every request.

app.use((req, res, next) => { console.log(' '); next(); });

Request Handling

POST with JSON· Handle POST with payload.

app.post('/users', (req, res) => { const { name } = req.body; res.status(201).json({ id: 1, name }); });

Error Handling

Error middleware· Catch errors globally.

app.use((err, req, res, next) => { console.error(err.stack); res.status(500).json({ error: 'Broken' }); });

Testing

Supertest· Integration test.

import request from 'supertest';
import app from '../app';
it('returns users', async () => {
  const res = await request(app).get('/users');
  expect(res.status).toBe(200);
});