Express Routing

What Express is

Express is the most-used Node web framework, a thin layer over http that does the chores you have been hand-rolling: route matching, params, query parsing, JSON responses. You install it from npm, Node's package registry:

npm install express

const express = require("express");
const app = express();

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

app.listen(3000);

Everything here is familiar. app.get("/users/:id", handler) is your routing table from lesson 3-2, :id is your matchPath with captures (req.params.id), the handler is a callback, and res.json sets the JSON header and stringifies for you.

What Express hands you on req

For a request to GET /posts?status=draft&page=2 matched by app.get("/posts", ...):

Note every value is a string. page arrives as "2", not 2.

That req.query object comes from parsing status=draft&page=2: split on &, then split each piece on =. You have written parsers twice already (lessons 1-3 and 3-2). Write this one and you will never wonder what a framework does with query strings again.