A Step-by-Step Guide to Handle Query Parameters in Node.js

Managing query parameters and query strings in a Node.js HTTP server without using external libraries like Express.js involves parsing the URL to extract these values. Here's a step-by-step guide on how to handle query parameters and query strings in your simple server:

Step 1: Modify the Router to Handle Query Parameters

Update router.js:

const url = require('url');
const querystring = require('querystring');

const routes = {
  '/': require('./routes/index'),
  '/about': require('./routes/about')
};

const router = (req, res) => {
  const parsedUrl = url.parse(req.url);
  const pathname = parsedUrl.pathname;
  const queryParams = querystring.parse(parsedUrl.query);

  req.queryParams = queryParams; // Attaching queryParams to the request object

  const handler = routes[pathname] || require('./routes/notFound');
  handler(req, res);
};

module.exports = router;

Step 2: Use Query Parameters in Route Handlers

Update routes/index.js to utilize query parameters:

const index = (req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');

  // Use query parameters if available
  const name = req.queryParams.name || 'World';
  res.end(`Hello, ${name}!\n`);
};

module.exports = index;

For demonstration, update routes/about.js to utilize query parameters:

const about = (req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');

  // Use query parameters if available
  const detail = req.queryParams.detail || 'default detail';
  res.end(`About Page: ${detail}\n`);
};

module.exports = about;

Step 3: Running the Server

In your terminal, restart the server:
```
node server.js
```
You should see the following output in your terminal:
```
Server running at http://127.0.0.1:3000/
```

Step 4: Testing Query Parameters

Open your web browser or use a tool like curl to test the server:
- Visit http://127.0.0.1:3000/?name=John to see the "Hello, John!" message.
- Visit http://127.0.0.1:3000/about?detail=specific%20info to see the "About Page: specific info" message.
- Visit http://127.0.0.1:3000/about to see the "About Page: default detail" message.

Explanation of the Code

Parsing URL:

Import the url and querystring modules:

const url = require('url');
const querystring = require('querystring');

Extracting Pathname and Query Parameters:
- In router.js:
```
const parsedUrl = url.parse(req.url);
const pathname = parsedUrl.pathname;
const queryParams = querystring.parse(parsedUrl.query);
```
  - url.parse(req.url) parses the URL and extracts the pathname and query string.
  - querystring.parse(parsedUrl.query) parses the query string into an object.
Attaching Query Parameters to Request Object:
```
req.queryParams = queryParams;
```
- Attach the parsed query parameters to the req (request) object for easier access in route handlers.
Using Query Parameters in Route Handlers:
- In routes/index.js:
```
const name = req.queryParams.name || 'World';
```
- In routes/about.js:
```
const detail = req.queryParams.detail || 'default detail';
```
  - Retrieve and use query parameters within the route handlers.