ssential Express Request Properties Every Developer Should Know

When working on the backend of projects, handling requests and responses is crucial. Managing these requests efficiently is essential for smooth communication between the client and server. Here are some common and important request properties that every developer should be familiar with.

1. req.ip

req.ip in Express.js is a property of the request object that provides the IP address of the client making the request. It returns a string representing the client's IP address.

Handling Proxies:
By default, if the app is behind a proxy, req.ip might return the IP of the proxy rather than the real client's IP. To get the correct client IP, you can configure Express to trust the proxy by setting trust proxy.

app.set("trust proxy", true);

Now, req.ip will return the correct IP of the client even when behind a proxy.

Example:

app.get('/', (req, res) => {
  console.log(req.ip);  // Logs the client's IP address
  res.send(`Your IP address is ${req.ip}`);
});

2. req.cookies

To use req.cookies we need to install the package called cookie-parser middleware. The property is use to get cookies sent by the client in Cookies header. Cookies in the req.cookies are unsigned, means they are not been tempered with or verified. You can use this for less sensitive data

import cookieParser from "cookie-parser";

app.use(cookieParser());

app.get('/example', (req, res) => {
  console.log(req.cookies);  // { cookieName: 'cookieValue' }
});

3. req.signedCookies

To use req.signedCookies we need to install the package called cookie-parser middleware. This contains cookies that have been signed and verified to ensure they haven't been altered. A signed cookies are encrypted with the secret key. The req.signedCookies store only the cookies which passes verification.

How to Set Signed Cookies:
To set a signed cookie, you can use the signed: true option:

res.cookie('signedCookieName', 'signedValue', { signed: true });

Example:

import cookieParser from "cookie-parser";

app.use(cookieParser('your-secret-key'));

app.get('/example', (req, res) => {
  console.log(req.signedCookies);  // { signedCookieName: 'signedValue' }
});

4. req.params

req.params in Express.js is an object that contains route parameters from the URL of the request. Route parameters are named placeholders in the route path, and req.params stores the values provided by the client in the URL for those placeholders.
You can define a route with parameters by using a colon (:) before the parameter name.

Example:

app.get('/users/:userId', (req, res) => {
  console.log(req.params); // { userId: 'valueFromURL' }
  res.send(`User ID is ${req.params.userId}`);
});

5. req.query

req.query in Express.js is an object that contains the query string parameters from the URL of the request. Query strings are key-value pairs that come after the ? in a URL and are used to pass additional data to the server. Multiple queries can be pass using &.

Example URL:

http://example.com/search?term=flowers&sort=asc

Example:

app.get('/search', (req, res) => {
  console.log(req.query);  // { term: 'flowers', sort: 'asc' }
  res.send(`Search term: ${req.query.term}, Sort order: ${req.query.sort}`);
});

6. req.body

It contains key-value pairs of data sent by the client. By default, its value is undefined. The body data can be populated using built-in middleware such as express.json and urlencoded({ extended: true }), or external middleware like body-parser.

The following code help you to understand

import express from "express";

const app = express();

app.use(express.json());
app.use(express.urlencoded({ extended: true }));

app.get("/user", (req, res) => {
    const user  = req.body;
    consolo.log(user);
    res.send(user);
})

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