[fix] refactor navigation singletons to avoid storing undefined refer…

…ence (#3374)

Co-authored-by: Rich Harris <hello@rich-harris.dev>
Co-authored-by: Bjorn Lu <bjornlu.dev@gmail.com>
Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

.changeset/brown-mangos-tie.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+[fix] refactor navigation singletons to avoid storing undefined reference

packages/kit/src/runtime/app/navigation.js

@@ -1,8 +1,6 @@
-import { router as router_, renderer } from '../client/singletons.js';
+import { router, renderer } from '../client/singletons.js';
 import { get_base_uri } from '../client/utils.js';
 
-const router = /** @type {import('../client/router').Router} */ (router_);
-
 /**
  * @param {string} name
  */

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

@@ -1,4 +1,7 @@
-/** @type {import('./router').Router?} */
+/**
+ * The router is nullable, but not typed that way for ease-of-use
+ * @type {import('./router').Router}
+ */
 export let router;
 
 /** @type {import('./renderer').Renderer} */
@@ -11,6 +14,6 @@ export let renderer;
  * }} opts
  */
 export function init(opts) {
-	router = opts.router;
+	router = /** @type {import('../client/router').Router} */ (opts.router);
 	renderer = opts.renderer;
 }