This little helper can save/load data into files for easy access.

cache_helper.js

module.exports = function(opts){
    var fs = require('fs')
        ,md5 = require('MD5')
        ,_ = require('underscore')
        ,cache_helper = {}
        ,settings = _.extend({
            cache_dir: __dirname + '/cache/'
        }, opts || {})
        ,timenow = function(){ 
            return (new Date()).getTime();
        }
    ;
    
    cache_helper.get_contents = function(name){
            //get the real filename
        var cache_filename = this.generate_filename(name)
            //check if the file exists yet
            ,exists = fs.existsSync(cache_filename)
        ;

        if (exists){
            return JSON.parse(fs.readFileSync(cache_filename, 'UTF-8')) || false;
        }
        else{
            return false;
        }
    };

    cache_helper.is_stale = function(name){
        var data = this.get_contents(name)
        ;

        if (data){
            return timenow() > data.meta.created + data.meta.stale_after;
        }
        else{
            return true;
        }
    };

    cache_helper.generate_filename = function(name, duration){
        return settings.cache_dir + name + '.json';
    };

    cache_helper.generate_meta = function(name, duration){
        var meta = {
            name: name
            ,stale_after: duration
            ,created: (new Date()).getTime()
            ,touched: null
        };

        return meta;
    }

    cache_helper.store = function(data, name, duration, overwrite){
            //get the real filename
        var cache_filename = this.generate_filename(name, duration)
            //check if the file exists yet
            ,exists = fs.existsSync(cache_filename)
            ,store_data = {
                meta: this.generate_meta(name, duration)
                ,data: data
            }
        ;

        //we only want to store if it doesn't exist yet or it does and we have
        //permission to overwrite it. we should also check if it has expired
        if (!exists || (exists && overwrite)){
            fs.open(cache_filename, 'w', function(err, fd){
                fs.write(fd, JSON.stringify(store_data));
            });
        }
    };

    cache_helper.fetch = function(name, fn){
        var file_data = this.get_contents(name)
        ;

        if (file_data){
            return file_data.data;
        }
        else{
            return false;
        }
    };

    //purge - or remove - existing cache files
    //can take a @partial_match value which will be used to check filenames and only
    //those containing the @partial_match will be removed
    cache_helper.purge = function(partial_match){
        var files = fs.readdirSync(settings.cache_dir)
            ,files_removed = 0
        ;

        _.each(files, function(filename){
            var remove = !partial_match;

            //simple partial match
            if (partial_match){
                remove = filename.toLowerCase().indexOf(partial_match.toLowerCase()) > -1;
            }

            if (remove){
                fs.unlinkSync(settings.cache_dir + filename);
                files_removed++;
            }
        });

        console.log('cache purge complete.', files.length + ' cache files found,', files_removed + ' files purged');
    };

    return cache_helper;
}