Caching

SPF uses a hybrid response cache: an in-memory LRU for the current session, plus a Cache API durable tier that survives reloads, so back/forward navigations to previously visited pages can be served without the network.

Eligibility rules

The cache policy is SPF's classic split between new and history navigations, controlled by one rule:

• a cached response is eligible only for history (back/forward) navigations — unless cache-unified is enabled;
• a prefetched response is eligible for one subsequent new navigation, then downgrades to history-only (one-shot semantics);
• new navigations otherwise always hit the server — the freshness guarantee.

A server may override the stored type per response with cacheType (new | history | prefetch) and address entries with cacheKey.

The two tiers

In-memory LRU (spf.cache) — fastest tier; entries expire after cache-lifetime ms and the LRU is capped at cache-max entries.

Durable tier (spf.cache.persistent) — the Cache API (modern-spf cache store). Written on every navigation; serves history navigations on a miss in memory. The durable tier only serves history navigations (unless cache-unified), preserving the "new navigations hit the server" guarantee.

Lookup order: memory → durable → network.

Public API

Method	Signature	Purpose
get	(url, navType) → SingleResponse | null	Read an eligible entry (consumes prefetch).
set	(url, response, type?) → string	Store a response; returns the cache key.
remove	(key) → void	Remove by cache key or response.cacheKey, incl. durable.
clear	() → void	Clear both tiers.
size	() → number	Live entry count.
durableGet	(url, navType) → Promise<SingleResponse | null>	Durable-tier lookup honoring the policy.
persistent	{ put, match, delete }	Raw Cache API tier access.

See Cache API reference for details.

Configuration

Key	Default	Meaning
cache-lifetime	600000 (10 min)	Entry lifetime in ms.
cache-max	50	LRU entry cap.
cache-unified	false	When true, cached responses serve all navigations.