HTTP caching

A session caches http: and https: responses according to their caching headers the way a private browser cache does:

• It uses a fresh response without making a request.
• It revalidates a stale response that has an ETag or Last-Modified header, so it doesn’t download an unchanged document again.
• Concurrent requests for the same URL share one request.

The HTTP cache is different from the documents a session keeps. A session keeps every document it retrieves, so reading through a session never shows a change. The HTTP cache belongs to the Hyperjump, so every session from that Hyperjump uses the same HTTP cache. When you start a new session to see changes, the new session only retrieves what has changed. For more information, see Sessions.

Where the cache keeps responses

Where the cache keeps responses by default depends on the environment:

Environment	Default
Node.js	In memory for the life of the Hyperjump
Browsers	No cache of its own because the browser already caches

To keep responses somewhere else, use the httpCache config:

TypeScript

import { FileHttpCacheStore, Hyperjump } from "@hyperjump/browser";

// Keep responses on disk so they outlive the process
const h = new Hyperjump({
  httpCache: new FileHttpCacheStore("./.cache/hyperjump")
});

Without httpCache, a Hyperjump gets the default for its environment. To turn caching off, use httpCache: false.

To keep responses somewhere else such as Redis, implement HttpCacheStore. Entries are JSON, so you can store them anywhere. A store defines these asynchronous methods:

Method	Description
get(url)	Returns the entry for a request URL, or undefined if there isn’t one
set(url, entry)	Stores the entry for a request URL
delete(url)	Removes the entry for a request URL

Each Hyperjump has its own default store, so Hyperjumps only share a cache when you give them the same store.

The cache is private. A response to a request with one set of credentials can answer a request to the same URL with another set of credentials. Don’t share a store between Hyperjumps that send different credentials to the same URLs. For more information, see HTTP headers.