Altering headers

This example illustrates how to add, change, or delete headers sent in a request or returned in a response.

You can't modify the value of certain headers, such as server, eh-cache-tag, or eh-cdn-cache-control.

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-CIS-Functions-Hello", "Hello from CIS 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
}