Simon Willison’s Weblog

22nd July 2022 - Link Blog

Promise Maps. Egbert Teeselink describes a neat JavaScript caching pattern: instead of caching key:value cache key:promise-that-resolves-to-value—doing this gives you dog piling prevention for free, because the first lookup of a value trigers the computation to fetch it while subsequent lookups wait on the same promise to resolve—or resolve instantly if the computation has completed.