Caching and consistency with Etags

To optimize GET requests, and only send JSON over the wire when it changed, you can configure to enable Etags. Etags also prevent so-called mid-air collisions, where a client tries to update en item that has been updated by another client in the meantime:

const config = {
  etags: true,
}
const server = await create(config)

After enabling etags, every GET request will return an etag response header, which clients can (optionally) send as an If-None-Match header with every subsequent GET request. Only if the resource changed in the meantime the server will return the new JSON, and otherwise it will return a 304 Not Modified response with an empty response body.

For updating or deleting items with a PUT, PATCH, or DELETE, after enabling etags, these requests are required to provide an If-Match header with the etag. Only if the etag represents the latest version of the resource the update is made, otherwise the server responds with a 412 Precondition Failed status code.