feat: support sveltekit apps on non-http protocols

.changeset/dirty-impalas-glow.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Added support for loading sveltekit apps on non-http protocols (eg: the `about:` protocol used on iframes that are populated via srcdoc)

packages/kit/src/runtime/client/utils.js

@@ -315,6 +315,11 @@ export function is_external_url(url, base, hash_routing) {
 			return false;
 		}
 
+		// be lenient if serving from an iframe via srcdoc
+		if (url.protocol === 'about:') {
+			return false;
+		}
+
 		// be lenient if serving from filesystem
 		if (url.protocol === 'file:' && url.pathname.replace(/\/[^/]+\.html?$/, '') === base) {
 			return false;

packages/kit/src/runtime/server/page/render.js

@@ -109,7 +109,8 @@ export async function render_response({
 			}
 		} else if (options.hash_routing) {
 			// we have to assume that we're in the right place
-			base_expression = "new URL('.', location).pathname.slice(0, -1)";
+			// if we are not on an http protocol (eg: about: protocol on iframes) we default to an empty string. Otherwise an error would be thrown by the URL constructor
+			base_expression = `location.protocol.slice(0, 4) === "http" ? new URL(${s(base)}, location).pathname.slice(0, -1) : ""`;
 		}
 	}