Express Fundamentals

Express is a small framework around Node HTTP. It removes repetitive routing code and adds middleware.

A Basic App

Install Express, create an app, and listen on a port.

import express from "express";

const app = express();

app.get("/", (request, response) => {
  response.send("Hello from Express");
});

app.listen(3000, () => {
  console.log("Server running on port 3000");
});

JSON Bodies

Register express.json() before routes that read a JSON body.

app.use(express.json());

app.post("/students", (request, response) => {
  const { name, level } = request.body;

  if (!name) {
    return response.status(422).json({ error: "name is required" });
  }

  response.status(201).json({ id: 1, name, level });
});

Middleware

Middleware is a function that runs before the route. Use it for logging, authentication and error handling.

function logger(request, response, next) {
  console.log(request.method, request.url);
  next();
}

app.use(logger);

Practice

1. Create an Express app with two GET routes.
2. Add express.json() and a POST route.
3. Write middleware that adds a request time header.

Hands-on exercise

Build an Express app with:
1. GET /students returning an array of two students.
2. POST /students accepting name and level and returning 201.
3. A 422 response when name is missing.

Recap

Express adds routing, JSON parsing and middleware to Node. Register middleware before the routes that need it.