node-cache getOrSet caching pattern.

cache.js

var NodeCache = require('node-cache');
var myCache = new NodeCache();

var cache = {

    /** Gets key from cache if exists, else sets the cache and returns data.
     * @param {string} cacheKey - Key to get or set.
     * @param {integer} timeout - Timeout (in seconds) for cache to release.
     * @param {Function} fn - Function to get data if key does not exist.
     * @param {Function} callback - Callback function to send back data or value.
     */
    getOrSet: function(cacheKey, timeout, fn, callback) {
    	myCache.get(cacheKey, function(err, value) {
    		if (!err) {
    			if (value == undefined) {

                    fn(function(data) {
    				    myCache.set(cacheKey, data, timeout);
                        callback(data);
                    });
    			} else {
                    callback(value);
    			}
    		}
    	});
    }
}

module.exports = cache;

example.js

var express = require('express');
var cache = require('./cache');
var router = express.Router();

var Spotify = require('./spotify');

router.get('/playlists', function(req, res) {

	var cacheKey = 'featured_playlists';
	var timeout = 60 * 15; // 15 minutes.

	cache.getOrSet(cacheKey, timeout, getFeaturedPlaylists, function(data) {
		res.json({data: data});
	});

	// Cache function.
	function getFeaturedPlaylists(callback) {
	    // Get playlists.
        var spotifyService = new Spotify();
	    spotifyService.getFeaturedPlaylists(function(data) {
            callback(data);
		});
	}
});

module.exports = router;