level-cache-tools

Three different cache types, backed by leveldb.

SimpleCache

Just get and put. Simple.

MemoizeCache

Memoize an asynchronous function to disk.

If you have a Twitter bot that gets sentences from news stories, for example, you could memoize the news story retrieval function with the URL as the key like so:

function newsStory(url, cb) {
  request.get(url, function (err, response, body) {
    cb(body);
  });
}

var memoizedNewsStory = new MemoizeCache('news-stories', newsStory);

// 1st call is not cached, this call stores it to disk via leveldb
memoizedNewsStory('http://cnn.com/blah', console.log);

// 2nd call is cached, retrieved from leveldb rather than hitting the network
memoizedNewsStory('http://cnn.com/blah', console.log);

ValueCache

Keep track of whether a value has been used or not.

Let's say you have a Twitter bot that composes tweets from a corpus of sentences and you don't want it to repeat itself. You can store values swith put() and query if they've been previously used with contains().

To keep trying until an unused value is found you could use async.detect or async.detectSeries:

var usedCandidates = new ValueCache('used-candidates');

// mark 'a' as used
usedCandidates.put('a', function (err) {
  var candidates = ['a', 'b', 'c'];

  async.detectSeries(candidates, usedCandidates.contains, function (result) {
    // result should equal 'b'
  });
});

TODO: Move the above example to ValueCache as firstUnused()?