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)

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