acache

npm install acache

Sometimes you want to:

1. make an async call to get some data
2. but use a cache if possible

Getting this right requires:

• creating an LRU
• a locking mechanism, so a bunch of calls for the same data on a cold cache don't cause multiple executions of your expensive function for the same data
• an easy uncaching call

This little lib makes it easy.

Coffeescript example using a database call (but really, any expensive async call works).

ac.query always calls back with (err, result).

{ACache} = require 'acache'

ac = new ACache {maxAgeMs: 10000, maxStorage: 100}

# pick a string for the cache key:

key = "#{uid}-#{friend_uid}"

# say, get something from the database, given 2 uid's
ac.query {
  keyBy: key
  fn: (cb) ->
    mysql.query 'SELECT BLEAH WHERE FOO=? AND BAR=?', [uid, friend_uid], (err, rows, info) ->
      res = {rows, info}
      cb err, res
}, defer err, res

# remove something from the cache
ac.uncache {keyBy: key}

# manually add something
ac.put {keyBy: key}, val

# check some basic stats
console.log ac.stats() # size, hits, misses, etc.

Curious if the cache was hit

It calls back with a 3rd boolean param, whether the cache was hit:
ac.query {
  keyBy: whatever
  fn: (cb) -> cb null, "hello world"
}, defer err, res, did_hit

constructor params:

• maxAgeMs: max time to store something in cache
• maxStorage: max answers to cache

query params:

• arg0 (object):
  • keyBy : a key for this cache call. Feel free to pass a string, number, or object; it will be hashed
  • fn : a function to run, to fill the cache, if it's missing. your function should take one parameter, cb. It should then call cb with err, res
• arg1 (fn) :
  • a function you want called with the results of your fn. Say, err, res from either the cache or hot read

Errors

This does not cache errors. If you want to cache errors you can easily call back with null, {err, res}.