docs: Clarify popstate handling to prevent UI freeze on navigation spam (#25)

Author: Ala-Ben-Aissia

exercises/04.router/05.problem.cache/ui/index.js

@@ -61,6 +61,7 @@ function Root() {
 
 			// 🐨 change this to setContentKey(historyKey)
 			startTransition(() => setContentPromise(nextContentPromise))
+			// 🐨 otherwise, setContentKey(historyKey) directly (no transition needed)
 		}
 		window.addEventListener('popstate', handlePopState)
 		return () => window.removeEventListener('popstate', handlePopState)

exercises/04.router/05.solution.cache/ui/index.js

@@ -56,9 +56,10 @@ function Root() {
 				const fetchPromise = fetchContent(nextLocation)
 				const nextContentPromise = createFromFetch(fetchPromise)
 				contentCache.set(historyKey, nextContentPromise)
+				startTransition(() => setContentKey(historyKey))
+			} else {
+				setContentKey(historyKey)
 			}
-
-			startTransition(() => setContentKey(historyKey))
 		}
 		window.addEventListener('popstate', handlePopState)
 		return () => window.removeEventListener('popstate', handlePopState)