Simple single resource cache.

-resourceCache.js

const isNotExpired = x => x && x.exp >= Date.now()

export function resourceCache (get, isValid = isNotExpired, initialData = undefined) {
  let data = initialData
  let pending = null

  return async () => {
    if (pending) return pending

    if (!isValid(data)) {
      try {
        pending = get()
        data = await pending
      } finally {
        pending = null
      }
    }

    return data
  }
}

README.md

Example:

import { resourceCache } from './resourceCache'

// Given a resource resolver, create one that auto caches
const getAuth = resourceCache(async () => {
  // Fetch the resource
  const token = await fetchApiToken()
  
  // Expire it after 5 minutes
  const exp = Date.now() + (5 * 60 * 1000)
  
  return { token, exp }
})

export async function fetchMyApi(path, options, retryOn401 = true) {
  const auth = await getAuth()
  
  const response = await fetch(baseURL + path, {
    ...options,
    headers: {
      Authorization: `Bearer ${auth.token}`,
      ...options?.headers,
    }
  })
  
  if (retryOn401 && response.status === 401) {
    // Invalidate used `auth` and retry.
    auth.exp = 0
    return fetchMyApi(path, options, false)
  }

  if (!response.ok) { ... }
  
  return response.json()
}