task-cache

a very small library to implement a cache layer over a function implementing ReaderTaskEither signature. Heavily inspired by Avenger.

install

yarn

yarn add task-cache

npm

npm install -S task-cache

quick start

Create a function with the readerTaskEither signature, wrap it with getUseRTAHook and use the resulting hook in your components:

import { getUseRTAHook } from "task-cache/react"
import { right } from "fp-ts/Either"

type Input = { token: string }
const getUser = (i: Input) => () => Promise.resolve(right({ name: "Mario" }))
const userHook = getUseRTAHook(getUser, { shouldRefetch: () => false })

const Username: React.FC = () => {
  const [user, invalidate] = userHook({ token: "123abc" })

  return user._tag === "success" ? (
    <>
      <div>`Hi ${user.value.name}!`</div>
      <button onClick={() => invalidate({ token: "123abc" })}>Logout</button>
    </>
  ) : (
    <div>Loading...</div>
  )
}

Using the react utility getUseRTAHook you get back a RemoteData<E, A>, while using the lower lavel api cached you get back a function with the same signature as the original one.

CacheStrategy

Out of the box task-cache provides you a very simple "cache-first" strategy where JSON stringification is used to determine input equality (important to determine where to store cached values) and cached value is always used (if found):

import { string } from "fp-ts"
import { pipe } from "fp-ts/function"
import { contramap } from "fp-ts/Eq"

const eqJson = pipe(
  string.Eq,
  contramap((v) => JSON.stringify(v)),
)
const defaultCacheStrategy = {
  inputEq: eqJson,
  shouldRefetch: () => false,
}

if you have different needs you can provide your own implementation of CacheStrategy, for example you may want to invalidate the cache every X minutes:

import { getUseRTAHook } from "task-cache/react"
import { either, option } from "fp-ts"

type Input = { token: string }
const getUser = (i: Input) => () => Promise.resolve(either.right({ name: "Mario" }))
const userHook = getUseRTAHook(getUser, {
  shouldRefetch: (lastValue) =>
    pipe(
      lastValue,
      option.fold(
        () => true,
        (v) => Date.now() - v.timestamp > 5000,
      ),
    ),
})

or you may need a custom inputEquality. In the following example two cached functions are joined toghether by sequencing, in this situation the resulting ReaderTaskEither will have both inputs (zum and bar) in its signature and would invalidate both rta and rta2 with the default strategy, therefore we use custom ones:

import { string } from "fp-ts"
import { pipe } from "fp-ts/function"
import { contramap } from "fp-ts/Eq"
import { cached } from "task-cache"
import { sequenceS } from "fp-ts/lib/Apply"

const inputEq = pipe(
  string.Eq,
  contramap((s: { bar: string }) => s.bar),
)
const inputEq2 = pipe(
  string.Eq,
  contramap((s: { zum: string }) => s.zum),
)

const rta = (_: { bar: string }) => {
  return taskEither.right({ foo: 1 })
}
const rta2 = (_: { zum: string; bar: string }) => {
  return taskEither.right({ bar: [1] })
}

const [cachedRTA] = cached(rta, { inputEq })
const [cachedRTA2] = cached(rta2, { inputEq: inputEq2 })

const product = sequenceS(readerTaskEither.readerTaskEither)({ cachedRTA, cachedRTA2 })

const result = product({ bar: "baz", zum: "foo" })()

cached

hooks are not the only utility exposed by the library, if you are not using react you can use the lower level cached to create you own implementation:

import { cached } from "task-cache"

const getFoo = (_: { bar: string }) => {
  return taskEither.right({ foo: 1 })
}

const [cachedRTA, invalidate] = cached(getFoo)

const result = await product({ bar: "baz" })()
const result2 = await product({ bar: "baz" })() // getFoo is not called, instead the cached value is returned
invalidate({ bar: "baz" })
const result2 = await product({ bar: "baz" })() // getFoo is called because the cached value for input { bar: "baz" } was invalidated

release flow

here you can find an explanation of the release flow.