Alter headers

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request));
});

async function handleRequest(request) {
  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;
}