Express.js Request Object

The request object in Express.js is an essential part of handling HTTP requests. It provides access to data sent by the client to the server and is used in routes to extract information like URL parameters, query strings, request body, and more.

 

Key Features of the Request Object

• Access to Request Data: Allows you to access data sent by the client, including URL parameters, query parameters, headers, and request body.
• HTTP Method: Provides access to the HTTP method (GET, POST, PUT, DELETE, etc.) used in the request.
• Route Parameters: Contains any parameters included in the URL path.
• Query Strings: Allows you to access the query parameters sent in the URL.
• Request Body: Used to extract data sent in the body of the request, particularly for POST and PUT methods.
• Request Headers: Allows you to inspect the headers sent with the request.

 

Components of the Request Object

req.params
The params object contains route parameters (dynamic values embedded in the URL). It is available when the route uses parameterized paths.

Example:

app.get('/user/:id', (req, res) => {
    const userId = req.params.id;
    res.send(`User ID: ${userId}`);
});

When a request is made to /user/123, the req.params.id will be '123'.

req.query
The query object contains the query string parameters (the key-value pairs after the ? in the URL). It is used for GET requests to send additional data.

Example:

app.get('/search', (req, res) => {
    const searchTerm = req.query.term;
    res.send(`Searching for: ${searchTerm}`);
});

For a request like /search?term=nodejs, the req.query.term will be 'nodejs'.

req.body
The body object is used to access data sent in the request body. This is particularly used with POST, PUT, or PATCH requests. You will need middleware like express.json() or express.urlencoded() to parse the body.

Example:

app.post('/submit', (req, res) => {
    const name = req.body.name;
    res.send(`Name received: ${name}`);
});

req.headers
The headers object contains the HTTP headers sent with the request. You can use it to access metadata like content type, authorization tokens, etc.

Example:

app.get('/headers', (req, res) => {
    const userAgent = req.headers['user-agent'];
    res.send(`User-Agent: ${userAgent}`);
});

req.method
The method property tells you the HTTP method used for the request (e.g., GET, POST, PUT, DELETE).

Example:

app.get('/method', (req, res) => {
    res.send(`Request method: ${req.method}`);
});

req.url
The url property contains the full URL of the request, including the path and query string.

Example:

app.get('/url', (req, res) => {
    res.send(`Request URL: ${req.url}`);
});

req.cookies
If the cookie-parser middleware is used, you can access cookies sent by the client via the cookies object.

Example:

app.get('/cookies', (req, res) => {
    const userCookie = req.cookies.user;
    res.send(`User Cookie: ${userCookie}`);
});

 

Common Use Cases

Accessing Route Parameters
If your route includes dynamic segments (e.g., /user/:id), you can access the value of :id using req.params.

Handling Query Strings
Query strings are often used to send additional data in a GET request, such as search terms or filters. You can retrieve query string values via req.query.

Handling POST Data
POST requests typically send data in the request body, such as form submissions. You can access this data via req.body after using the appropriate middleware.

Authentication
You can check the request headers for authentication tokens or session identifiers (e.g., using Authorization headers).

Debugging
To inspect the incoming request for debugging purposes, log various properties of req such as req.method, req.url, and req.headers.

 

Example Code

const express = require('express');
const app = express();
app.use(express.json());  // Middleware to parse JSON body

// Route with route parameter
app.get('/user/:id', (req, res) => {
    const userId = req.params.id;
    res.send(`User ID is: ${userId}`);
});

// Route with query string
app.get('/search', (req, res) => {
    const searchTerm = req.query.term;
    res.send(`Search term is: ${searchTerm}`);
});

// POST route to handle request body
app.post('/submit', (req, res) => {
    const { name, age } = req.body;
    res.send(`Name: ${name}, Age: ${age}`);
});

// Accessing headers
app.get('/headers', (req, res) => {
    const userAgent = req.headers['user-agent'];
    res.send(`User-Agent: ${userAgent}`);
});

// Start the server
app.listen(3000, () => {
    console.log('Server is running on port 3000');
});

 

Summary

The request object in Express.js is essential for handling client data in HTTP requests. It allows you to access route parameters, query strings, the request body, headers, and more. Understanding how to interact with this object is crucial for building dynamic and data-driven web applications.