Constructor parameters: ordered or options bag?

[js-choi]

Let’s assume that we make new classes rather than using Map and Set (see #8 and #5). Given that, we now have two or three possible parameters:

• A required string indicating the cache policy (#2), assuming that we go with #8. (If we go with Map.LRU etc. as per #5, then we would not have this parameter.)
• An optional positive integer indicating the cache’s max cardinality.
• An optional boolean, a string, or something that indicates whether to purge or cull itself in response to low-memory warnings from the host (#7).

There are several API choices that I can think of:

new CacheMap('lru', [ 256, 'purgeable' ], entries)
new CacheMap('lru', { maxSize: 256, purgeable: true }, entries)
new CacheMap('lru', entries, { maxSize: 256, purgeable: true })
new CacheMap('lru', { maxSize: 256, purgeable: true, entries })
new CacheMap({ policy: 'lru', maxSize: 256, purgeable: true, entries })

[ljharb]

Why separate classes rather than a constructor options bag parameter to the existing Map and Set?

[js-choi]

Reusing Map and Set and extending them with option bags is another API option. I’ve tweaked this issue’s original post to say that this issue assumes that we’re going with separate classes as per #8 or #5.

I’m inclined to agree with https://github.com/tc39/proposal-policy-map-set/issues/1#issuecomment-1199766146, but we probably should talk about that more in #1.