How to Set Response Headers in Node.js: Simple Guide

In Node.js, you set response headers using the res.setHeader(name, value) method on the response object. This method lets you specify the header name and its value before sending the response to the client.

Syntax

The basic syntax to set a response header in Node.js is:

• res.setHeader(name, value): Sets a single header where name is the header name (string) and value is the header value (string or array of strings).
• You must call this before sending the response body.

javascript

res.setHeader('Content-Type', 'text/html');

Example

This example shows a simple HTTP server that sets the Content-Type and Cache-Control headers before sending a response.

javascript

import http from 'http';

const server = http.createServer((req, res) => {
  res.setHeader('Content-Type', 'text/plain');
  res.setHeader('Cache-Control', 'no-cache');
  res.writeHead(200);
  res.end('Hello, world!');
});

server.listen(3000, () => {
  console.log('Server running at http://localhost:3000/');
});

Output

Server running at http://localhost:3000/

Common Pitfalls

Common mistakes when setting response headers include:

• Calling res.setHeader after res.end() or res.writeHead() which sends the headers immediately.
• Setting the same header multiple times without using an array for multiple values.
• Using incorrect header names or values that do not follow HTTP standards.

javascript

import http from 'http';

const server = http.createServer((req, res) => {
  // Wrong: setting header after response is sent
  res.end('Done');
  res.setHeader('Content-Type', 'text/plain'); // This will have no effect
});

Quick Reference

Method	Description
res.setHeader(name, value)	Sets a response header before sending the response
res.getHeader(name)	Retrieves the value of a response header
res.removeHeader(name)	Removes a previously set header
res.writeHead(statusCode, headers)	Sets status code and headers at once before sending response

Key Takeaways

Always set headers using res.setHeader() before sending the response body.

Headers must be valid HTTP header names and values.

Do not set headers after calling res.end() or res.writeHead().

Use res.writeHead() to set status and headers together if preferred.

Check headers with res.getHeader() and remove with res.removeHeader() if needed.