A generic expiring cache

cache.js

Cache = function(cleanupIntervalMS) {
  if (typeof cleanupIntervalMS === 'undefined')
    cleanupIntervalMS = 1000 * 60 * 5; // 5 minute default interval
  
  if (cleanupIntervalMS)
    this.cleanupTimer = setInterval(this.cleanup, cleanupIntervalMS);
};

Cache.prototype = {
  store: {},
  
  /**
   * key - Key of the value to retrieve.
   * insertCallback(fn) - Fired when the key is not found in the cache and no
   *   lookup is currently running for the requested key. fn expects three
   *   parameters: an error message (or null), the value to cache, and the
   *   cache lifetime in milliseconds.
   * foundCallback(err, value) - Fired when the key is resolved to a value.
   */
  get: function(key, insertCallback, foundCallback) {
    var obj = this.store[key];
    
    if (obj) {
      if (obj.callbacks)
        return obj.callbacks.push(foundCallback);
      else if (obj.expiration <= +new Date())
        delete this.store[key];
      else
        return foundCallback(null, obj.value);
    }
    
    obj = { callbacks: [foundCallback] };
    this.store[key] = obj;
    
    insertCallback(function(err, newValue, lifetimeMS) {
      for (var i = 0; i < obj.callbacks.length; i++)
        value.callbacks[i](err, newValue);
      
      obj.value = newValue;
      obj.expiration = new Date() + lifetimeMS;
      this.store[key] = obj;
    });
  },
  
  cleanup: function() {
    var now = +new Date();
    
    for (var key in this.store) {
      var obj = this.store[key];
      if (obj.expiration && obj.expiration <= now)
        delete this.store[key];
    }
  },
};

module.exports = Cache;