getOrCreate() method

[rstacruz]

This seems like a very common use case, and in fact it's the preferred way you use a cache in Rails. Is there any reason it's not implemented?

cache.getOrCreate(key, () => { expensive computation })

Where:

LRU.prototype.fetch = function (key, fn) {
  if (this.has(key)) return this.get(key)
  var result = fn()
  this.set(key, result)
  return result
}

[airliti]

Not implementing a .getOrCreate method could even be a possible issue ( and as demonstrated with your implementation )! The timing between the #.has and #.get method could be just surpassing the maxAge resulting in an undefined value. I did an implementation for an LruCache for myself and a possible solution can be found through visiting https://github.com/airliti/estructura/blob/master/src/lib/LruCache.js#L457.

If your interested, I've got sample code to prove the problem.

[isaacs]

I'd accept a fetch method like you describe.

I'm not worried about the time resolution of TTL expiring, this is primarily a lru cache anyway.

[isaacs]

Proof of concept if anyone wants to pick this up and write tests for it: https://github.com/isaacs/node-lru-cache/blob/isaacs/get-or-fetch-return-stale-while-fetching/index.js