app.post
- Node.js course
- Intermediate
- Lesson 27/116
- 5 min
Learn to define POST routes with app.post.
app.post
app.post(path, handler) defines a POST route. It works like app.get but listens for POST requests. POST is usually used to submit data (forms, APIs).
To read the POST request's body you use req.body. But Express does not parse the body by default; you must add the JSON middleware with app.use(express.json()). Example: app.post("/data", (req, res) => { res.json({ received: req.body.name }); });. Here req.body.name reads the sent name value. res.json sends an object as a JSON response; the content type is automatically application/json.
req.body and express.json()
The POST request's body is read with req.body. But Express does not parse it by default. For a JSON body you add the app.use(express.json()) middleware.
Example: app.use(express.json()); app.post("/data", (req, res) => { console.log(req.body); res.json({ received: req.body.name }); });. When the client sends { "name": "Alex" }, req.body.name becomes Alex. The express.json() middleware turns the incoming JSON string into an object and puts it on req.body. Without it req.body is undefined. A middleware is a function that runs between the request and the route.
Practice Define a POST route
Import express and create app. Add the JSON middleware with app.use(express.json()). Define a POST route with app.post("/data", (req, res) => res.json({ received: req.body.name })). The ready-made code below starts the server and sends a POST request with body { name: "Alex" }.
Starter code
// Import express, create app and add JSON middleware
// write here
// Read the name from the "/data" POST route and respond
// write here
const server = app.listen(3000, () => {
const http = require("http");
const opts = { hostname: "localhost", port: 3000, path: "/data", method: "POST", headers: { "Content-Type": "application/json" } };
const r = http.request(opts, (res) => {
let body = "";
res.on("data", (c) => body += c);
res.on("end", () => { console.log("Reply: " + body); server.close(); });
});
r.write(JSON.stringify({ name: "Alex" }));
r.end();
});Sample solution
const express = require("express");
const app = express();
app.use(express.json());
app.post("/data", (req, res) => { res.json({ received: req.body.name }); });
const server = app.listen(3000, () => {
const http = require("http");
const opts = { hostname: "localhost", port: 3000, path: "/data", method: "POST", headers: { "Content-Type": "application/json" } };
const r = http.request(opts, (res) => {
let body = "";
res.on("data", (c) => body += c);
res.on("end", () => { console.log("Reply: " + body); server.close(); });
});
r.write(JSON.stringify({ name: "Alex" }));
r.end();
});Expected output
Yanıt: {"alindi":"Ayşe"}
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is app.post used for?
app.post("/data", handler)- GET isteklerini dinler
- Closes the server
- POST isteklerini dinler Correct answer
- Loads the module
Explanation: app.post listens for POST requests.
2 Match each piece to its role
| Term | Meaning |
|---|---|
app.post |
Defines a POST route |
req.body |
Reads the body |
express.json() |
Parses the body |
res.json |
Sends a JSON response |
3 Complete the req.body access
res.json({ alindi: req.____.ad });res.json({ alindi: req.body.ad });Explanation: req.body accesses the body.