$http Service Caching in AngularJS 1.8.2: Missing Timeout Constraint for Stale Data During Migration

Answer for this migration case

In AngularJS 1.8.2 there is no built-in timeout or TTL for $http caching. The safest migration-safe approach is to stop using cache:true for the affected endpoints and replace it with a custom $cacheFactory instance that stores a timestamped wrapper. A request/response interceptor then checks age against a configurable maxAge and bypasses or refreshes stale entries. For the live migration window, force a one-time eviction and then re-enable caching with the wrapper.

Confirmed facts

• $http with cache:true uses a $cacheFactory instance keyed by URL and params.
• $cacheFactory in 1.8.2 provides put, get, remove and removeAll. It has no expiration semantics.
• Expiry must be implemented by application code wrapping stored values.

Likely explanation

Stale data after migration is likely because cached responses remain valid indefinitely until manually evicted. The UI will keep reading the old $cacheFactory entry even after the server has changed.

Steps needed for this case

1. Identify the cache used. Inspect $http config to confirm which requests use cache:true versus a custom cache object, and which $cacheFactory instance is shared.
2. Create a dedicated cache for mutable endpoints:

   var ttlCache = $cacheFactory('apiTtlCache');

3. Wrap responses with a timestamp. In a response interceptor for those endpoints, store {data: response, ts: Date.now()} in ttlCache under the $http cache key.
4. Check age on read. In a request interceptor, if a cached wrapper exists, compare Date.now() - entry.ts to a configurable maxAge. If stale, delete the entry and let the request go to the server, or return the stale value and trigger a background refresh.
5. Migration cutover. Immediately after deployment, call ttlCache.removeAll() or remove keys for the migrated endpoints, then re-enable the TTL wrapper. This avoids serving pre-migration data.

A custom interceptor can reliably track and invalidate stale entries. It adds a small CPU cost per hit for the timestamp check and a memory cost for the wrapper. Always-revalidate interceptors negate caching benefits and increase load during live migration, so use maxAge rather than forced revalidation.

Third-party libraries

Community wrappers for AngularJS 1.x historically added TTL semantics on top of $cacheFactory. Compatibility with 1.8.2 and current maintenance status is variable and must be verified before adoption. No officially supported TTL is provided by AngularJS core.

Assumption: you are on AngularJS 1.8.2 and the cache is client-side only. Verification needed: confirm which endpoints share a cache instance and whether they can be isolated. That detail changes whether a global interceptor or per-service cache is appropriate.