Some improvement ideas that would be useful (expire cache immediately, and user session cache)

[skliffmueller]

I have been using this module with great success in an express app. The middleware functionality does just about everything I need it to, except for two things which I will list below.

First, the ability to clear the cache based off a key would be awesome. I was able to make a quick hack to accomplish this before creating the middleware by the following (Basicly this just sets the TTL to 0):

const Cache = require('stale-multi-cache');

const opts = {
  name: 'key',
  staleTTL: 300,
  maxItems: 300,
  bypassHeader: 'bypass',
};

// Hack to force cache expire
function expireKey(key) {
  return this.get(key).then(raw => {
    let json = JSON.parse(raw);
    return this.createValueAndMultiSet(key, json.value, {
      staleTTL:0,
      expireTTL:0
    })
  })
}
Cache.prototype.expireKey = expireKey;

module.exports = new Cache([new Cache.LRUMemoryStore({max: opts.maxItems})], opts);

Next, there are situations where the cache results would be different depending on what user session is signed in. The ability to have the key generate based off a user session, or any additional key options on the middleware would be awesome.

My idea on this would be to allow a key object handler as an option on
https://github.com/kelsin/stale-multi-cache/blob/master/src/cache.js#L193
And every time getKey is called at
https://github.com/kelsin/stale-multi-cache/blob/master/src/cache.js#L209
It will check to see if handler exists, execute handler, or stick with the default.