req.params

req.params is an object holding values captured from named segments in the route path.

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

app.get("/products/:productId", (req, res) => {
    res.send(`Viewing product ${req.params.productId}`);
});

app.listen(4600, () => console.log("Listening on 4600"));

A GET request to /products/88 gives req.params.productId === "88".

Common uses

• Reading resource IDs from a URL.
• Building nested resources, like /authors/:authorId/books/:bookId.
• Powering dynamic RESTful routes.