Route Parameters and Query Strings

Route Parameters and Query Strings

Route parameters are named URL segments prefixed with a colon. Express parses them automatically and exposes them on req.params as an object of strings.

app.get("/posts/:postId/comments/:commentId", (req, res) => {
  const { postId, commentId } = req.params;
  res.json({ postId, commentId });
});

Query strings appear after the ? in a URL and are parsed into req.query. Every value arrives as a string (or an array of strings for repeated keys), so you must convert to numbers explicitly when needed.

// GET /products?category=shoes&page=2
app.get("/products", (req, res) => {
  const category = req.query.category as string;
  const page = Number(req.query.page) || 1;
  res.json({ category, page });
});