Caching AJAX

apiRequest : function(requestURL, requestHandler){
            /*Sends an AJAX request to the specified requestURL and uses the requestHandler to respond
             *The requestHandler recieves the api request in a json as a parameter and may be used as such
             *All API requests use GET requests
             */
            if(this.supports_storage()){
                var apiUrl = requestURL.removeParams();
                if(typeof this.cachedURL(apiUrl) == "undefined" || !this.cachedURL(apiUrl)){
                    console.log("fetching data");
                    var xmlHttp = null;
                    xmlHttp = new XMLHttpRequest();
                    xmlHttp.onreadystatechange = function(){
                        //Call the handler
                        if(typeof xmlHttp.responseText != "undefined"){
                            if(xmlHttp.readyState==4 && xmlHttp.status==200){
                                var result = JSON.parse(xmlHttp.responseText);
                                console.log(typeof this);
                                requestHandler(result);
                                //Add resulting json from api to local storage
                                localStorage.setItem(apiUrl,JSON.stringify(result))
                                //Mark as cached
                                if(typeof fins.cachedURLs == "undefined"){
                                    fins.cachedURLs = {};
                                }
                                fins.cachedURLs[apiUrl] = true;
                            }
                        }
                    };
                    xmlHttp.open( "GET", requestURL, true );
                    xmlHttp.send( null );

                }else{
                    //The result is cached so we should go ahead and give that to the function
                    console.log("using cache");
                    requestHandler(JSON.parse(localStorage.getItem(apiUrl)))    ;
                }
            }else{
                throw new Error("Local browser storage no supported, use more modern browser");
            }
        },

        apiSendData : function(sendURL,requestHandler){
            var xmlHttp = null;
            xmlHttp = new XMLHttpRequest();
            xmlHttp.onreadystatechange = function(){
                //Convert the response to JSON first.
                if(typeof xmlHttp.responseText != "undefined"){
                    requestHandler(JSON.parse(xmlHttp.responseText));
                }
            };
            xmlHttp.open( "GET", sendURL, true );
            xmlHttp.send( null );
            //Mark the url that maps to retrieving this data
            if(typeof apiURLMaps[sendURL] == "undefined"){
                throw new Error("Invalid API request in fins:apiSendData, no mapping exists");
            }
            //Mark the corresponding retrievel request for the sending action as dirty and in need of being recached
            cachedURLs[apiURLMaps[sendURL]] = false;

        },