Host bucket of a cache key, for the per-host concurrency cap: the origin host of
an absolute URL key (https://host/... → host), or the empty string for a
synthetic key with no :// (e.g. an upsample fill, which does no fetch of its own
— grouping them costs nothing). Avoids new URL (which throws on relative keys
and is far slower than a couple of indexOfs called once per pending request).
Host bucket of a cache key, for the per-host concurrency cap: the origin host of an absolute URL key (
https://host/...→host), or the empty string for a synthetic key with no://(e.g. an upsample fill, which does no fetch of its own — grouping them costs nothing). Avoidsnew URL(which throws on relative keys and is far slower than a couple ofindexOfs called once per pending request).