Returns data from cache if available; otherwise executes the specified function and places the results in cache before returning the data.

cache.js

var redis = require('redis');

function Cache(port, host, options) {
    this.client = redis.createClient(port, host, options);
};

// Returns data from cache if available;
// otherwise executes the specified function and places the results in cache before returning the data.
Cache.prototype.fetch = function(key, func, options, callback) {
    // Options are optional
    if(!callback) {
        callback = options;
    }

    this.client.get(key, function(err, data) {
        if(err) {
            return callback(err);
        }

        if(data) {
            return callback(null, JSON.parse(data));
        }

        var client = this.client;

        func(function(err, data) {
            if(err) {
                return callback(err);
            }

            // Default expire time is 30 to 60 seconds
            var expire = (options && options.expire) ? options.expire : Math.floor(Math.random() * (60000 - 30000 + 1) + 30000); 
            client.psetex(key, expire, JSON.stringify(data));

            return callback(null, data);
        });
    });
};

exports.createClient = function(port, host, options) {
    return new Cache(port, host, options);
};


// Usage
var cache = require('./cache').createClient(6379, 'localhost');
var request = require('request');

cache.fetch('what-is-my-ip', function(callback) {
    request.get('http://ip.jsontest.com', { json: true }, callback);
}, function(err, ip) {
    console.log(ip);
});