A cache system.

Example

let data = await cache(
  // list of cache files to validate
  // the first valid cache file in order will be considered
  ["./report-today.json", "./report-yesterday.json"],
  // an optional data source to fetch the fresh cache data in case of no valid cache file is found
  () => fetch("https://my-server.com/getReport"),
  {
    // the maximum time period before considering a file as expired.
    maxAge: 1000,
    // a fallback to be used in case of the dataSource function failed to refresh the cache.
    // in this case, it accepts a recently expired cache
    maxStale: 2000,
    // a callback that is called to read the cache value
    // it may read from file system, memory, database, or any other source.
    // in real-life usage, you may need to iterate over all entries to find the first cache hit.
    read: (entries) => readFile(`./cache/${entries[0]}`),
    // a callback that is called if all cache sources are expired,
    // and the dataSource retrieved the fresh data successfully.
    write: (entry, data) => writeFile(`./cache/${entry}`, JSON.stringify(data)),
  },
);

If you plan to save the cached data in file-system, check out cacheFS()