combine async / promise calls and cache result in memory with LRU

import memoAsync from 'memo-async'

const getUserInfo = memoAsync(   // <- magic
  async (userId) => {
    const { data } = await fetcher('http://xxx/', { userId })
    return data
  }
)

// parallel requests

const infos = await Promise.all([
  getUserInfo(12),   // send request
  getUserInfo(12),   // (cached) re-use 1st request
  getUserInfo(9),    // send request
  getUserInfo(12),   // (cached) re-use 1st request
])

// then request again

const user5 = await getUserInfo(12)   // get cached result,
                                      // or send request if last request failed

// after seconds...

const user6 = await getUserInfo(12)   // send request (cache expired)

this package provides memoAsync, which can be a utility function, or a decorator:

• memoAsync(fn, opts) returns an wrapped async function, which may combine calls and cache result in memory.

  • fn : Function - your async function
  • opts : MemoOptions - optional, see below

• memoAsync(opts) returns a class method decorator

  • opts : MemoOptions - optional, see below

  Note: each instance has its own LRU cache in memory by default.

  If you have many instances, consider using exact one LRUCache by setting opts.cache. Meanwhile, do not forget writing a opts.genKey

  decorator example

  class Reporter {
    @memoAsync()
    async readData(filename) {
      // some expensive requests
    }
  }
  
  const joe = new Reporter()
  // now joe.readData() may merge and cache requests

• genKey : (...args) => string

  compute the cache key from arguments.

  default: treat args as strings and concat them

  if you are using memoAsync within a class, you may use this while computing

• duration : number

  duration of one batch, aka. how long a result can be cached.

  default: 3000 (ms)

• batchSize : number

  how many requests (invoking) can be merged into one.

  default: 500 (# req)

• cache : LRUCache

  use an existing lru-cache instance.

  if not set, memoAsync will create one.

• cacheSize : number

  set the cache capacity. works when cache is not given.

  default: 1000

• onHit : (key, result, args) => void callback when cache is hit.

  • key : string the cache key

  • result : Promise the cached Promise. you cannot change it

  • args : any[] array of arguments

  Note: if you are using memoAsync within a class, this will be set.