app.post()

// Basic syntax for a POST route
app.post(path, handler);

// Specifying multiple handlers
app.post(path, middleware, handler);

Without registering middleware, req.body will be undefined for POST request bodies. Register one of the following via app.use() in advance, depending on the format of the submitted data.

The following examples cover basic POST route definitions, retrieving JSON bodies and form data, and using multiple handlers with validation in between.

var express = require('express');
var app = express();

// --- Register middleware ---

// Register middleware to parse JSON request bodies
app.use(express.json());

// Register middleware to parse HTML form submission request bodies
app.use(express.urlencoded({ extended: true }));

// --- Basic POST route ---

// Register a new user on POST requests to /users
app.post('/users', function(req, res) {
    // Access the request body via req.body (requires express.json())
    var name = req.body.name;
    var email = req.body.email;
    console.log('Received data:', name, email);
    // Respond with status code 201 (Created)
    res.status(201).json({ message: 'Registered successfully', name: name, email: email });
});

// --- Receiving submissions from an HTML form ---

// Route corresponding to a form with action="/login" method="POST"
app.post('/login', function(req, res) {
    // With express.urlencoded() registered, form data is available via req.body
    var username = req.body.username;
    var password = req.body.password;
    if (username === 'admin' && password === 'secret') {
        // Redirect to the dashboard on successful authentication
        res.redirect('/dashboard');
    } else {
        // Return 401 on failed authentication
        res.status(401).json({ error: 'Incorrect username or password' });
    }
});

// --- Combining URL parameters and request body ---

// Add a comment to /posts/:id/comments (e.g., /posts/42/comments)
app.post('/posts/:id/comments', function(req, res) {
    // Retrieve the URL parameter via req.params.id
    var postId = req.params.id;
    // Retrieve the comment body via req.body.text
    var text = req.body.text;
    res.status(201).json({ postId: postId, comment: text });
});

// --- Multiple handlers with validation ---

// Define a middleware function to validate input values
function validateUser(req, res, next) {
    var name = req.body.name;
    var email = req.body.email;
    // Check that both name and email are present
    if (!name || !email) {
        // Return 400 and stop processing if either is missing
        return res.status(400).json({ error: 'name and email are required' });
    }
    // If validation passes, call next() to pass control to the next handler
    next();
}

// Only requests that pass validateUser reach the registration handler
app.post('/members', validateUser, function(req, res) {
    res.status(201).json({ message: 'Member registered successfully', data: req.body });
});

// --- Start the server ---

app.listen(3000, function() {
    console.log('Server started: http://localhost:3000');
});

app.post() is the most fundamental way to receive POST requests. To access req.body, you must register a body-parsing middleware (express.json() or express.urlencoded()) via app.use() beforehand. If you forget to register it, req.body will be undefined.

By using a middleware chain with multiple handlers, you can insert shared processing such as validation and authentication into each route. Calling next() passes control to the next handler; if it is not called, processing stops at that point.

As your application grows larger, you can use express.Router() to split routes across files, making your code easier to organize. See also app.get() for how to define GET routes.