ajax pass-thru cache

ajaxCache.js

    var ajaxCache = function(cfg){
  	this._cache  = {};
		this._pk     = cfg.pk||null;
		this._prefix = cfg.prefix||'';
    };

    ajaxCache.prototype = {
    	constructor: ajaxCache,

    	set: function(key, val) {
    		this._cache[key] = val;
    	},

    	get: function(key) {
    		return this.exists(key) ? this._cache[key] : null;
    	},

    	exists: function(key) {
    		return key in this._cache;
    	},

		fetch: function(method, url, data, callback, type) {
			if ( $.isFunction( data ) )
			{
				type     = type || callback;
				callback = data;
				data     = undefined;
			}
			var self = this
				key  = this._pk ? this._pk+':'+data[this._pk] : url;
			 	key  = this._prefix + key;
			
			
			if (this.exists(key))
			{
				return callback.call(this, self.get(key));
			}
			return $.ajax({
				url: url,
				type: method,
				dataType: type,
				data: data,
				success: function(data) {
					self.set(key, data);
					callback.call(this, data);
				}
			});
		},
		load: function(url, data, callback, type) {
			this.fetch('get', url, data, callback, type );
		},
		post: function(url, data, callback, type) {
			this.fetch('post', url, data, callback, type );
		}
  };

Usage.js

var aCache = new ajaxCache({pk: "folder_id", prefix: "folder");

$('#folder_sel').change(function() {
  var folder_id = $(this).val();
  aCache.post(href_val, {'folder_id': folder_id}, function(data) {
	  //code
  });
})