docs: Add example reverse proxy handler for Facebook Pixel (#648)

docs/facebook-pixel.md

@@ -21,6 +21,43 @@ Set the script element's `type` attribute to `text/partytown`. For example:
 
 The `connect.facebook.net` response does not provide the correct CORS header, and a reverse proxy should be used. Below is an example of setting the `resolveUrl` config to proxy the `connect.facebook.net` requests. Please see [Proxying Requests](/proxying-requests) for more information.
 
+## Proxying with Server Handlers
+
+If you're using a server framework like Nuxt 3, you can handle proxying dynamically using API routes. Below is an example configuration that dynamically fetches resources based on the provided URL and returns the response with appropriate headers:
+
+```js
+export default defineEventHandler(async (event) => {
+  const query = getQuery(event);
+  const url = String(query?.url) || null;
+
+  if (!url || !url.includes("connect.facebook.net")) {
+    throw createError({
+      status: 500,
+      message: "Invalid URL",
+    });
+  }
+
+  // Fetch the file content dynamically based on the URL
+  const response = await $fetch(url).catch((error) => {
+    throw createError({
+      status: 500,
+      message: `Failed to fetch resource: ${error.message}`,
+    });
+  });
+
+  setResponseHeaders(event, {
+    "Access-Control-Allow-Origin": "*", // Ensures proper CORS handling
+    "Access-Control-Allow-Headers": "Content-Type, Authorization",
+    "Access-Control-Allow-Methods": "POST, GET, OPTIONS, PUT, DELETE",
+    "Content-Type": "application/x-javascript; charset=utf-8",
+    "Cache-Control":
+      "public, max-age=5, s-maxage=5, stale-if-error=2678400, stale-while-revalidate=86400", // Add necessary caching headers
+  });
+
+  return response;
+});
+```
+
 ## Forward Events
 
 Facebook Pixel uses the [fbq()](https://www.facebook.com/business/help/402791146561655?id=1205376682832142) function to send events. In order for Partytown to forward the calls to `window.fbq({..})`, the forward config should add `"fbq"`. Please see [forwarding events and triggers](/forwarding-events) for more information.