Node.js Response Reference
HTTP Response Object
The HTTP Response object in Node.js (http.ServerResponse) is created internally by an HTTP server, not by the user. It's passed as the second parameter to the 'request' event callback function.
This object is used to return data to the client and implements the Writable Stream interface. The response object is how the server sends data back to the client that made the request.
Using the Response Object
const http = require('http');
// Create an HTTP server
const server = http.createServer((req, res) => {
// 'res' is the ServerResponse object
res.statusCode = 200;
res.setHeader('Content-Type', 'text/plain');
res.end('Hello World\n');
});
server.listen(8080, () => {
console.log('Server running at http://localhost:8080/');
});
Run example »
Response Properties
| Property | Description |
|---|---|
| response.finished | A boolean indicating if the response has completed. |
| response.headersSent | A boolean indicating if headers were sent to the client. |
| response.sendDate | When true, the Date header will be automatically generated and sent in the response if it's not already set. Default: true. |
| response.statusCode | The status code that will be sent to the client (e.g., 200, 404, 500). |
| response.statusMessage | The status message that will be sent to the client. |
| response.socket | Reference to the underlying socket. |
| response.writableEnded | A boolean indicating whether response.end() has been called. |
| response.writableFinished | A boolean indicating if all data has been flushed to the underlying system. |
Response Methods
| Method | Description |
|---|---|
| response.addTrailers(headers) | Adds HTTP trailing headers to the response. |
| response.cork() | Forces buffering of data written to the response. |
| response.end([data[, encoding]][, callback]) | Signals to the server that all response headers and body have been sent. |
| response.flushHeaders() | Flushes the response headers. |
| response.getHeader(name) | Gets the value of an outgoing header that's already been queued but not sent. |
| response.getHeaderNames() | Returns an array containing the names of headers that have been queued for an outgoing message. |
| response.getHeaders() | Returns a shallow copy of the current outgoing headers. |
| response.hasHeader(name) | Returns true if the header identified by name is currently set. |
| response.removeHeader(name) | Removes a header that's queued for sending. |
| response.setHeader(name, value) | Sets a single header value for the header object. |
| response.setTimeout(msecs[, callback]) | Sets the timeout value of the socket. |
| response.uncork() | Flushes the data buffered by cork(). |
| response.write(chunk[, encoding][, callback]) | Sends a chunk of the response body. |
| response.writeContinue() | Sends an HTTP/1.1 100 Continue message to the client. |
| response.writeHead(statusCode[, statusMessage][, headers]) | Sends a response header to the request. |
| response.writeProcessing() | Sends an HTTP/1.1 102 Processing message to the client. |
Basic Response Example
A basic example of using various response methods:
const http = require('http');
// Create an HTTP server
const server = http.createServer((req, res) => {
// Set status code and message
res.statusCode = 200;
res.statusMessage = 'OK';
// Set headers
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Powered-By', 'Node.js');
// Log response information
console.log(`Response status: ${res.statusCode} ${res.statusMessage}`);
console.log(`Headers sent: ${res.headersSent}`);
// Send additional headers using writeHead (overwrites previously set ones)
res.writeHead(200, {
'Content-Type': 'text/html',
'X-Custom-Header': 'Custom Value'
});
// Check headers sent now
console.log(`Headers sent after writeHead: ${res.headersSent}`);
// Write response body in chunks
res.write('<!DOCTYPE html>\n');
res.write('<html>\n');
res.write('<head><title>Node.js Response Example</title></head>\n');
res.write('<body>\n');
res.write(' <h1>Hello from Node.js!</h1>\n');
res.write(' <p>This response was sent using the ServerResponse object.</p>\n');
res.write('</body>\n');
res.write('</html>');
// End the response
res.end();
// Log completion status
console.log(`Response finished: ${res.finished}`);
console.log(`Response writableEnded: ${res.writableEnded}`);
console.log(`Response writableFinished: ${res.writableFinished}`);
});
// Start the server
const PORT = 8080;
server.listen(PORT, () => {
console.log(`Server running at http://localhost:${PORT}/`);
});
Run example »
Setting Response Headers
Different ways to set response headers:
const http = require('http');
// Create HTTP server
const server = http.createServer((req, res) => {
// Method 1: Set individual headers with setHeader
res.setHeader('Content-Type', 'application/json');
res.setHeader('Cache-Control', 'max-age=3600');
res.setHeader('X-Custom-Header', 'Method 1');
// Get a header value
const contentType = res.getHeader('Content-Type');
console.log(`Content-Type header: ${contentType}`);
// Check if a header exists
console.log(`Has Cache-Control header: ${res.hasHeader('Cache-Control')}`);
// Get all header names
console.log('Header names:', res.getHeaderNames());
// Get all headers as an object
console.log('All headers:', res.getHeaders());
// Remove a header
res.removeHeader('X-Custom-Header');
console.log(`After removal, has X-Custom-Header: ${res.hasHeader('X-Custom-Header')}`);
// Method 2: Set multiple headers with writeHead
res.writeHead(200, {
'Content-Type': 'application/json',
'X-Custom-Header': 'Method 2',
'X-Powered-By': 'Node.js'
});
// Send JSON response
const responseObject = {
message: 'Headers demonstration',
headers: Object.fromEntries(
Object.entries(res.getHeaders())
),
headersSent: res.headersSent
};
res.end(JSON.stringify(responseObject, null, 2));
});
// Start server
const PORT = 8080;
server.listen(PORT, () => {
console.log(`Server running at http://localhost:${PORT}/`);
});
Run example »
HTTP Status Codes
Setting different HTTP status codes:
const http = require('http');
const url = require('url');
// Create an HTTP server that demonstrates different status codes
const server = http.createServer((req, res) => {
// Parse the request URL
const parsedUrl = url.parse(req.url, true);
const path = parsedUrl.pathname;
// Set Content-Type header
res.setHeader('Content-Type', 'text/html');
// Handle different paths with different status codes
if (path === '/') {
// 200 OK
res.writeHead(200, 'OK');
res.end(`
<h1>HTTP Status Codes Demo</h1>
<p>This page demonstrates different HTTP status codes.</p>
<ul>
<li><a href="/">200 OK (this page)</a></li>
<li><a href="/redirect">301 Moved Permanently</a></li>
<li><a href="/not-modified">304 Not Modified</a></li>
<li><a href="/bad-request">400 Bad Request</a></li>
<li><a href="/unauthorized">401 Unauthorized</a></li>
<li><a href="/forbidden">403 Forbidden</a></li>
<li><a href="/not-found">404 Not Found</a></li>
<li><a href="/server-error">500 Internal Server Error</a></li>
</ul>
`);
}
else if (path === '/redirect') {
// 301 Moved Permanently
res.writeHead(301, {
'Location': '/'
});
res.end();
}
else if (path === '/not-modified') {
// 304 Not Modified
res.writeHead(304);
res.end();
}
else if (path === '/bad-request') {
// 400 Bad Request
res.writeHead(400, 'Bad Request');
res.end(`
<h1>400 Bad Request</h1>
<p>The server could not understand the request due to invalid syntax.</p>
<p><a href="/">Go back to home</a></p>
`);
}
else if (path === '/unauthorized') {
// 401 Unauthorized
res.writeHead(401, {
'WWW-Authenticate': 'Basic realm="Access to the site"'
});
res.end(`
<h1>401 Unauthorized</h1>
<p>Authentication is required but was not provided.</p>
<p><a href="/">Go back to home</a></p>
`);
}
else if (path === '/forbidden') {
// 403 Forbidden
res.writeHead(403, 'Forbidden');
res.end(`
<h1>403 Forbidden</h1>
<p>The server understood the request but refuses to authorize it.</p>
<p><a href="/">Go back to home</a></p>
`);
}
else if (path === '/not-found') {
// 404 Not Found
res.writeHead(404, 'Not Found');
res.end(`
<h1>404 Not Found</h1>
<p>The requested resource could not be found on this server.</p>
<p><a href="/">Go back to home</a></p>
`);
}
else if (path === '/server-error') {
// 500 Internal Server Error
res.writeHead(500, 'Internal Server Error');
res.end(`
<h1>500 Internal Server Error</h1>
<p>The server has encountered a situation it doesn't know how to handle.</p>
<p><a href="/">Go back to home</a></p>
`);
}
else {
// Default: 404 Not Found
res.writeHead(404, 'Not Found');
res.end(`
<h1>404 Not Found</h1>
<p>The requested resource could not be found on this server.</p>
<p><a href="/">Go back to home</a></p>
`);
}
});
// Start the server
const PORT = 8080;
server.listen(PORT, () => {
console.log(`Server running at http://localhost:${PORT}/`);
});
Run example »
Streaming Responses
Using the response object to stream data:
const http = require('http');
const fs = require('fs');
const path = require('path');
// Create an HTTP server
const server = http.createServer((req, res) => {
const parsedUrl = new URL(req.url, 'http://localhost');
const pathname = parsedUrl.pathname;
// Handle different paths
if (pathname === '/') {
// Send a regular response
res.writeHead(200, {'Content-Type': 'text/html'});
res.end(`
<h1>Streaming Examples</h1>
<ul>
<li><a href="/stream-text">Stream a large text response</a></li>
<li><a href="/stream-file">Stream a file</a></li>
<li><a href="/stream-json">Stream a JSON response</a></li>
</ul>
`);
}
else if (pathname === '/stream-text') {
// Stream a large text response
res.writeHead(200, {'Content-Type': 'text/plain'});
let count = 1;
const max = 10;
// Write response in chunks with delay
const interval = setInterval(() => {
res.write(`Chunk ${count} of data\n`.repeat(20));
if (count >= max) {
clearInterval(interval);
res.end('\nStreaming complete!');
}
count++;
}, 500);
// Handle client disconnect
req.on('close', () => {
clearInterval(interval);
console.log('Client closed connection');
});
}
else if (pathname === '/stream-file') {
// Create a sample file
const filePath = path.join(__dirname, 'sample-large-file.txt');
if (!fs.existsSync(filePath)) {
const writeStream = fs.createWriteStream(filePath);
for (let i = 0; i < 10000; i++) {
writeStream.write(`Line ${i}: This is a sample line of text for streaming demonstration.\n`);
}
writeStream.end();
}
// Get file stats
const stat = fs.statSync(filePath);
// Set headers
res.writeHead(200, {
'Content-Type': 'text/plain',
'Content-Length': stat.size
});
// Create read stream and pipe to response
const fileStream = fs.createReadStream(filePath);
fileStream.pipe(res);
// Handle file stream errors
fileStream.on('error', (err) => {
console.error(`Error streaming file: ${err.message}`);
res.end('Error streaming file');
});
// Clean up after response is sent
res.on('finish', () => {
fs.unlink(filePath, (err) => {
if (err) console.error(`Error deleting sample file: ${err.message}`);
});
});
}
else if (pathname === '/stream-json') {
// Stream a large JSON response
res.writeHead(200, {'Content-Type': 'application/json'});
// Start JSON array
res.write('[\n');
let count = 0;
const max = 100;
let isFirst = true;
// Write JSON objects with delay
const interval = setInterval(() => {
// Add comma for all but first item
if (!isFirst) {
res.write(',\n');
} else {
isFirst = false;
}
// Create a JSON object
const obj = {
id: count,
name: `Item ${count}`,
timestamp: new Date().toISOString(),
data: `Sample data for item ${count}`
};
// Write the object as JSON
res.write(JSON.stringify(obj, null, 2));
if (count >= max) {
clearInterval(interval);
// End JSON array
res.write('\n]');
res.end();
}
count++;
}, 100);
// Handle client disconnect
req.on('close', () => {
clearInterval(interval);
console.log('Client closed connection during JSON streaming');
});
}
else {
// Handle unknown paths
res.writeHead(404, {'Content-Type': 'text/plain'});
res.end('Not Found');
}
});
// Start the server
const PORT = 8080;
server.listen(PORT, () => {
console.log(`Streaming server running at http://localhost:${PORT}/`);
});
Run example »
Compression
Compressing responses with gzip or deflate:
const http = require('http');
const zlib = require('zlib');
// Create an HTTP server with compression
const server = http.createServer((req, res) => {
// Get the Accept-Encoding header
const acceptEncoding = req.headers['accept-encoding'] || '';
// Create a sample response (large string)
const sampleData = 'This is a sample text that will be compressed. '.repeat(1000);
// Function to send the response with appropriate headers
function sendResponse(data, encoding) {
// Set Content-Encoding header if compression is used
if (encoding) {
res.setHeader('Content-Encoding', encoding);
}
res.setHeader('Content-Type', 'text/plain');
res.setHeader('Vary', 'Accept-Encoding');
res.writeHead(200);
res.end(data);
}
// Check what encodings the client supports
if (/\bgzip\b/.test(acceptEncoding)) {
// Client supports gzip
console.log('Using gzip compression');
zlib.gzip(sampleData, (err, compressed) => {
if (err) {
console.error('Gzip compression failed:', err);
sendResponse(sampleData); // Fall back to uncompressed
} else {
sendResponse(compressed, 'gzip');
console.log(`Original size: ${sampleData.length}, Compressed size: ${compressed.length}`);
console.log(`Compression ratio: ${(compressed.length / sampleData.length * 100).toFixed(2)}%`);
}
});
} else if (/\bdeflate\b/.test(acceptEncoding)) {
// Client supports deflate
console.log('Using deflate compression');
zlib.deflate(sampleData, (err, compressed) => {
if (err) {
console.error('Deflate compression failed:', err);
sendResponse(sampleData); // Fall back to uncompressed
} else {
sendResponse(compressed, 'deflate');
console.log(`Original size: ${sampleData.length}, Compressed size: ${compressed.length}`);
console.log(`Compression ratio: ${(compressed.length / sampleData.length * 100).toFixed(2)}%`);
}
});
} else if (/\bbr\b/.test(acceptEncoding)) {
// Client supports Brotli (if Node.js version supports it)
if (typeof zlib.brotliCompress === 'function') {
console.log('Using Brotli compression');
zlib.brotliCompress(sampleData, (err, compressed) => {
if (err) {
console.error('Brotli compression failed:', err);
sendResponse(sampleData); // Fall back to uncompressed
} else {
sendResponse(compressed, 'br');
console.log(`Original size: ${sampleData.length}, Compressed size: ${compressed.length}`);
console.log(`Compression ratio: ${(compressed.length / sampleData.length * 100).toFixed(2)}%`);
}
});
} else {
console.log('Brotli not supported in this Node.js version');
sendResponse(sampleData); // Fall back to uncompressed
}
} else {
// No compression supported by client
console.log('No compression used');
sendResponse(sampleData);
}
});
// Start the server
const PORT = 8080;
server.listen(PORT, () => {
console.log(`Compression server running at http://localhost:${PORT}/`);
});
Run example »
Best Practices
- Always set Content-Type: Always set the appropriate Content-Type header for your responses.
- Use proper status codes: Use appropriate HTTP status codes to indicate the result of the request.
- Set proper headers: Set appropriate headers like Cache-Control, Content-Length, etc.
- Handle errors properly: Return appropriate status codes (4xx, 5xx) with meaningful error messages.
- Stream large responses: For large responses, use streaming instead of loading everything into memory.
- Implement compression: Use compression for text-based responses to reduce bandwidth usage.
- Security headers: Include security headers like Content-Security-Policy, X-Content-Type-Options, etc.
- Always end the response: Always call
response.end()to finalize the response.
