Syncing with a feed

Your app has a source of truth: an RSS feed, a course API, a list of map areas. collection.sync() reconciles stored items with it:

const feed = await (await fetch('/feed.json')).json();

const states = await episodes.sync(
  feed.items.map(({ guid, title, author }) => ({ id: guid, title, meta: { author } })),
  { prune: true },
);
// states[i] is the stored item for feed.items[i], or undefined if it isn't downloaded

What it does:

Updates title and meta of stored items whose values changed, emitting a change event with type: 'update'.
With prune: true, deletes stored items whose id isn’t in the list. Pinned items are kept.
Returns the current state for each input, in order, so you can render the list with download states in one pass.

sync() never starts downloads; it’s for bookkeeping. Combine it with your own policy, for example “keep the newest three episodes”:

const newest = feed.items.slice(0, 3);
await episodes.downloadAll(newest.map((ep) => ({ id: ep.guid, url: ep.enclosure.url, title: ep.title, size: ep.enclosure.length })));

With maxItems: 3 on the collection, older episodes are evicted as new ones arrive.