promiseMemo

Memoize an asynchronous function.

Usage

Memoize an asynchronous function, so that it only runs when a promise does not exist for the given arguments. If a promise is rejected, it will be removed from the cache.

import * as _ from 'radashi'

const calls = []

const getData = _.promiseMemo(async param => {
  calls.push(param)

  return new Promise(resolve => resolve(param))
})

const val1 = await getData(1)
const val2 = await getData(2)
const val3 = await getData(1)

console.log(calls) // [1, 2]

Expiration

The ttl option can be used to specify a time-to-live for the memoized value. If you call the memoized function after the TTL has expired, it will run the function again.

Even after the TTL has expired, the cached promise will remain in memory until you call the function again. This is a side effect of using a timestamp, rather than a timeout, to track the expiration.

import * as _ from 'radashi'

const calls = []

const getData = _.promiseMemo(
  async param => {
    calls.push(param)

    return new Promise(resolve => resolve(param))
  },
  {
    ttl: 1000,
  },
)

const val1 = await getData(1)
const val2 = await getData(2)

await _.sleep(2000)

const val3 = await getData(1)

console.log(calls) // [1, 2, 1]

Key Function

Use the key option to customize how the cache key is generated from the arguments. By default, JSON.stringify is used on the whole arguments array.

const memoized = _.promiseMemo(func, {
  key: arg => arg.user.id,
})

const resultA = await memoized({ user: { id: 'Alpha' } })
const resultA2 = await memoized({ user: { id: 'Alpha' } })

resultA === resultA2 // true