Understanding Express.js Request and Response Objects

Request Object in Express.js

The Request object in Express.js encapsulates all information about an incoming HTTP request. It provides access to request headers, parameters, query strings, and other request-related data.

const express = require('express');
const application = express();
application.listen(3000);

application.get('/profile/:uid', (request, response) => {
  // Original request URL string
  console.log("URL:", request.originalUrl);
  // Protocol string (http, https)
  console.log("Protocol:", request.protocol);
  // Client IP address
  console.log("IP:", request.ip);
  // URL path portion
  console.log("Path:", request.path);
  // Request hostname
  console.log("Host:", request.hostname);
  // HTTP method
  console.log("Method:", request.method);
  // Query string object
  console.log("Query:", JSON.stringify(request.query));
  // Check if request is fresh
  console.log("Fresh:", request.fresh);
  // Check if request is stale
  console.log("Stale:", request.stale);
  // Check for secure connection
  console.log("Secure:", request.secure);
  // Check charset support
  console.log("UTF8:", request.acceptsCharsets('utf8'));
  // Get specific header value
  console.log("Connection:", request.get('connection'));
  // All headers as object
  console.log("Headers:", JSON.stringify(request.headers, null, 2));
  
  response.send("Profile Data Retrieved");
});

Response Object in Express.js

The Response object handles the server's response to client requests. It provides methods for setting headers, status codes, and sending various types of response data.

Setting Headers

Response headers control how clients interpret the response. Express provides several methods for header manipulation:

// Get and set individual headers
const contentType = response.get('Content-Type');
response.set('Content-Type', 'text/plain');

// Set multiple headers at once
response.set({
  'Content-Type': 'application/json',
  'Cache-Control': 'no-cache'
});

// Set Location header for redirects
response.location('/login');

// Set Content-Type from file extension
response.type('html');

// Set Content-Disposition for file downloads
response.attachment('./documents/report.pdf');

Setting Status Codes

HTTP status codes idnicate the result of the request proecssing:

response.status(200); // OK
response.status(404); // Not Found
response.status(500); // Internal Server Error

Sending Responses

Multiple methods exist for sending different types of responses:

const express = require('express');
const application = express();
application.listen(3000);

application.get('/', (request, response) => {
  const htmlContent = '<html><body><h1>Welcome</h1></body></html>';
  
  response.status(200);
  response.set({
    'Content-Type': 'text/html',
    'Content-Length': Buffer.byteLength(htmlContent)
  });
  
  response.send(htmlContent);
});

application.get('/not-found', (request, response) => {
  response.status(404).send("Resource not found");
});

Sending JSON Responses

For API endpoints, JSON responses are commonly used:

application.get('/api/data', (request, response) => {
  // Configure JSON formatting
  application.set('json spaces', 2);
  
  response.json({
    institution: "Museum of Science",
    established: '1869',
    collectionSize: '34M',
    departments: ['astronomy', 'biology', 'paleontology', 'zoology']
  });
});

application.get('/api/error', (request, response) => {
  response.status(500).json({
    success: false,
    error: "Database connection failed"
  });
});

// JSONP for cross-domain requests
application.get('/api/jsonp', (request, response) => {
  application.set('jsonp callback name', 'callback');
  response.jsonp({
    data: "JSONP response"
  });
});

Sending Files

Express provides convenient methods for file transfers:

application.get('/download/:file', (request, response) => {
  const filename = request.params.file;
  
  response.download('./uploads/' + filename, filename, (error) => {
    if (error) {
      console.error("File transfer failed:", error);
      response.status(500).send("Download error");
    }
  });
});

application.get('/static/:asset', (request, response) => {
  const assetPath = request.params.asset;
  
  response.sendFile(assetPath, {
    root: './public',
    maxAge: 86400000 // 24 hours
  }, (error) => {
    if (error) {
      response.status(404).send("Asset not found");
    }
  });
});

Implementing Redirects

Redirects guide clients to different URLs:

application.get('/external', (request, response) => {
  response.redirect('https://example.com');
});

application.get('/old-path', (request, response) => {
  response.redirect('/new-path');
});

application.get('/new-path', (request, response) => {
  response.send("You've been redirected");
});

// Relative redirects
application.get('/section/first', (request, response) => {
  response.redirect('../second');
});

Tags: Express nodejs web-development javascript Backend

Posted on Wed, 16 Sep 2026 16:17:42 +0000 by phpforme

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