What is Immutable Hashed Assets?
Static files with content hashes in their filenames, emitted under the immutable build output. When code changes the hash changes, so browsers safely cache each version forever without risking stale JavaScript or styles.
Related terms
Cache-Control Headers
Response headers telling browsers and CDNs how long to reuse a file. This site serves its RSS feed with a one-hour public cache, while hashed static assets can carry far longer lifetimes because filenames change on rebuild.
Code-Splitting by Route
Automatic chunking of JavaScript per route so visitors download only what the current page needs. SvelteKit splits at route boundaries by default, keeping dashboard code out of marketing pages and initial loads lean.
Caching
Storing responses at the browser, CDN, or edge so repeat visits skip origin work. Correct cache headers and edge caching are usually the cheapest large performance win available.
SSR Per Request
Fresh HTML rendered on the server for every request, used for personalized or frequently changing pages. Server rendering guarantees complete markup on first paint but costs compute per visit, so reserve it for dynamic routes.
CSR Shell
A minimal HTML shell that renders content in the browser after JavaScript loads. Client rendering suits authenticated dashboards behind login, where SEO matters less and interactivity starts only after scripts execute.
Hydration Cost
The JavaScript work that turns server-rendered HTML into an interactive app. Hydration replays component logic in the browser, so oversized bundles delay input readiness even when paint looks instant.