This "TODO" code comment has been present from day-1 in the TypeScript source, still unresolved (time to file an issue!): https://github.com/readium/r2-streamer-js/blob/6afd2362c4e0eaa47bac2abac89340fdee52c2e1/src/http/server.ts#L353-L358 Basically, the cache of ReadiumWebPubManifest models grows indefinitely in the current implementation.