Update headers example (#1663)

Close #1661

Author: kristianfreeman

products/workers/src/content/examples/alter-headers.md

@@ -14,22 +14,28 @@ tags:
 </ContentColumn>
 
 ```js
-async function handleRequest(request) {
-  // Make the headers mutable by re-constructing the Request.
-  request = new Request(request)
-  request.headers.set("x-my-header", "custom value")
-  const URL = "https://examples.cloudflareworkers.com/demos/static/html"
-
-  // URL is set up to respond with dummy HTML
-  let response = await fetch(URL, request)
-
-  // Make the headers mutable by re-constructing the Response.
-  response = new Response(response.body, response)
-  response.headers.set("x-my-header", "custom value")
-  return response
-}
-
-addEventListener("fetch", event => {
+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
+}
 ```
+
+You can also use the [`custom-headers-example` template](https://github.com/signalnerve/custom-headers-example) to deploy this code to your custom domain.