SvelteKit and Cloudflare Compatibility Date after `2024-04-01`

Today, I needed to increase my compatibility_date for my Svelte project. I noticed, that when I ran the project locally with npx wrangler dev, that no POST requests worked any longer. There was a 405 Method Not Allowed HTTP error. The same was true when I opened the branch preview deployment.

tl;dr: I added the assets_navigation_has_no_effect compatibility flag. Now it works.

"$schema" = "./node_modules/wrangler/config-schema.json"

# …

compatibility_date = "2026-03-17"
compatibility_flags = ["nodejs_compat", "global_fetch_strictly_public", "assets_navigation_has_no_effect"]

# …

The problem is that Cloudflare changed how they invoke the worker with a compatibility date after 2024-04-01. Before, the worker was invoked for every request. After, the worker is not invoked if the request is a browser page navigation request. A fetch('/somepage') would invoke the worker, a navigation with <a href="/somepage"> wouldn’t.

I don’t quite get the logic, to be honest. Especially, why they stop passing POST requests to the worker in this mode. Now it is, what it is.

The compatibility flag assets_navigation_has_no_effect tells the Cloudflare Worker environment that the worker must be invoked everytime. In my case, I handle the caching on the CDN level anyway. So I don’t worry too much about the worker being invoked too often.