overlay

src/lib/utils/location.ts

@@ -76,6 +76,16 @@ interface ResolveLocationOptions {
 	};
 }
 
+/**
+ * Geocoding results for a route segment, kept for the life of the process.
+ *
+ * A city's coordinates do not change, and the same segment is resolved over and
+ * over: once per per-location route during the prerender (five builds of the
+ * same lookup for every city), and again on every client-side hop from a city's
+ * week page to its comparison or archive.
+ */
+const resolvedLocations = new Map<string, GeoLocation>();
+
 export async function resolveLocationFromRoute({
 	urlLocation,
 	routePrefix,
@@ -86,6 +96,11 @@ export async function resolveLocationFromRoute({
 		return coordinateLocation(parseFloat(coordMatch[1]), parseFloat(coordMatch[2]));
 	}
 
+	// The canonical-path check below still has to run per call (the same city is
+	// reached under different route prefixes), so only the lookup is cached.
+	const cached = resolvedLocations.get(urlLocation);
+	if (cached) return finishResolve(cached, routePrefix, event);
+
 	let urlLocationName: string;
 	let urlLocationId: string | undefined;
 
@@ -124,6 +139,15 @@ export async function resolveLocationFromRoute({
 		location = candidate;
 	}
 
+	resolvedLocations.set(urlLocation, location);
+	return finishResolve(location, routePrefix, event);
+}
+
+function finishResolve(
+	location: GeoLocation,
+	routePrefix: string,
+	event: ResolveLocationOptions['event']
+): GeoLocation {
 	// trailingSlash is 'always' (see routes/+layout.ts), so the router serves
 	// every path with a trailing slash. Match that here or the equality check
 	// never holds and the redirect loops forever. The comparison also has to