Cache functions that return promises with a TTL

memioze-with-ttl.js

/**
 * Memioze a function with a TTL
 * @param func {function} The function to memioze (can return promise)
 * @param ttl {number?} milliseconds to cache results (default = 30000)
 * @param ttlError {number?} milliseconds to cache errors (default = ttl = 30000)
 * @param initialValue {*} an optional value to return before initial func() result
 * @return {{get: (function(...[*]=): Promise<*>), clear: (function(): void)}}
 */
export function memoizeWithTTL ({ func, ttl = 30000, ttlError = ttl, initialValue }) {
  let cache = {}

  return {
    clear: (key) => {
      if (key) {
        cache[key] = { expires: 0, state: '', value: initialValue }
      } else {
        cache = {}
      }
    },

    get: async (...args) => {
      const cacheKey = crypto.createHash('sha1')
        .update(JSON.stringify(args))
        .digest('base64')

      cache[cacheKey] = cache[cacheKey] || { expires: 0, state: '', value: initialValue }
      const cachedItem = cache[cacheKey]

      // If TTL has expired then get the updated value from func
      if (cachedItem.expires < new Date().getTime() && cachedItem.state !== 'pending') {
        cachedItem.state = 'pending'
        try {
          cachedItem.value = await func(...args)
          cachedItem.expires = new Date().getTime() + ttl
          cachedItem.state = 'resolved'
        } catch (error) {
          cachedItem.value = error
          cachedItem.expires = new Date().getTime() + ttlError
          cachedItem.state = 'rejected'
        }
      }

      // Return the cached value
      if (cachedItem.state === 'rejected') {
        throw cachedItem.value
      }
      return cachedItem.value
    }
  }
}