Alter headers

JavaScript

export default {
  async fetch(request) {
    const response = await fetch("https://example.com");

    // Clone the response so that it's no longer immutable
    const newResponse = new Response(response.body, response);

    // Add a custom header with a value
    newResponse.headers.append(
      "x-workers-hello",
      "Hello from Cloudflare Workers",
    );

    // Delete headers
    newResponse.headers.delete("x-header-to-delete");
    newResponse.headers.delete("x-header2-to-delete");

    // Adjust the value for an existing header
    newResponse.headers.set("x-header-to-change", "NewValue");

    return newResponse;
  },
};

TypeScript

export default {
  async fetch(request): Promise<Response> {
    const response = await fetch(request);

    // Clone the response so that it's no longer immutable
    const newResponse = new Response(response.body, response);

    // Add a custom header with a value
    newResponse.headers.append(
      "x-workers-hello",
      "Hello from Cloudflare Workers",
    );

    // Delete headers
    newResponse.headers.delete("x-header-to-delete");
    newResponse.headers.delete("x-header2-to-delete");

    // Adjust the value for an existing header
    newResponse.headers.set("x-header-to-change", "NewValue");

    return newResponse;
  },
} satisfies ExportedHandler;

Python

from workers import Response, fetch

async def on_fetch(request):
    response = await fetch("https://example.com")

    # Grab the response headers so they can be modified
    new_headers = response.headers

    # Add a custom header with a value
    new_headers["x-workers-hello"] = "Hello from Cloudflare Workers"

    # Delete headers
    if "x-header-to-delete" in new_headers:
        del new_headers["x-header-to-delete"]
    if "x-header2-to-delete" in new_headers:
        del new_headers["x-header2-to-delete"]

    # Adjust the value for an existing header
    new_headers["x-header-to-change"] = "NewValue"

    return Response(response.body, headers=new_headers)

Hono

import { Hono } from 'hono';

const app = new Hono();

app.use('*', async (c, next) => {
  // Process the request with the next middleware/handler
  await next();

  // After the response is generated, we can modify its headers

  // Add a custom header with a value
  c.res.headers.append(
    "x-workers-hello",
    "Hello from Cloudflare Workers with Hono"
  );

  // Delete headers
  c.res.headers.delete("x-header-to-delete");
  c.res.headers.delete("x-header2-to-delete");

  // Adjust the value for an existing header
  c.res.headers.set("x-header-to-change", "NewValue");
});

app.get('*', async (c) => {
  // Fetch content from example.com
  const response = await fetch("https://example.com");

  // Return the response body with original headers
  // (our middleware will modify the headers before sending)
  return new Response(response.body, {
    headers: response.headers
  });
});

export default app;

You can also use the custom-headers-example template ↗ to deploy this code to your custom domain.