req.body

req.body holds the parsed body of an incoming request. It stays undefined until a body-parsing middleware — express.json() or express.urlencoded() — runs first.

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

app.use(express.json());

app.post("/comments", (req, res) => {
    console.log(req.body.text);
    res.send("Comment stored");
});

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

Sending { "text": "Great read!" } as JSON populates req.body.text with that string.

Common uses

• Reading form submissions (login, registration, contact forms).
• Reading JSON payloads sent by a frontend or another service.
• Reading fields from multi-part form data (usually alongside multer for file uploads).