Css Caching in sessionstorage

cache.js

var css_href_array = [];
			(function () {
			    "use strict";
			    // once cached, the css file is stored on the client forever unless
			    // the URL below is changed. Any change will invalidate the cache
				var styleTags = document.getElementsByClassName('js-style');
				function getBrowser() {
			        var myAgent = navigator.userAgent.toLowerCase();
			        if( myAgent.indexOf('msie') != -1 && parseInt(myAgent.split('msie')[1]) == 8 ){
			            return 'ie8';
			        }else{
			            return 'default';
			        }
			    }
				
				for( var i = 0; i < styleTags.length; i++ ){
					if( styleTags[i].getAttribute('data-font') ){
						css_href_array.push([styleTags[i].getAttribute('id'), styleTags[i].getAttribute('data-href') + getBrowser() + '.css' ]);
					}else{
						css_href_array.push([styleTags[i].getAttribute('id'), styleTags[i].getAttribute('data-href')]);
					}
				}
				
				//var css_href = '/static/css/fonts/web-font-' + getBrowser() + '.css';
				//css_href_array.push(['font_cache', css_href]);
				
			    // a simple event handler wrapper
			    function on(el, ev, callback) {
			        if ( el.addEventListener ) {
			            el.addEventListener(ev, callback, false);
			        } else if ( el.attachEvent ) {
			            el.attachEvent("on" + ev, callback);
			        }
			    }
		 
			    // if we have the fonts in sessionStorage or if we've cached them using the native browser cache
				for( var css in css_href_array ){
					if ( (window.sessionStorage && sessionStorage.getItem( css_href_array[css][0] )) || document.cookie.indexOf( css_href_array[css][0] ) > -1 ) {
				        // just use the cached version
				        injectFontsStylesheet(css_href_array[css]);
				    } else {
				        // otherwise, don't block the loading of the page; wait until it's done.
				        on(window, "load", injectFontsStylesheet(css_href_array[css]));
				    }
				}
		 
		 
			    // quick way to determine whether a css file has been cached locally
			    function fileIsCached(href) {
			        return window.sessionStorage && sessionStorage.getItem(href[0]);
			    }
		 
			    // time to get the actual css file
			    function injectFontsStylesheet( _fileArray ) {
			        // if this is an older browser
			        if ( !window.sessionStorage || !window.XMLHttpRequest ) {
			            var stylesheet = document.createElement('link');
			            stylesheet.href = _fileArray[1];
			            stylesheet.rel = 'stylesheet';
			            stylesheet.type = 'text/css';
			            document.getElementsByTagName('head')[0].appendChild(stylesheet);
			            // just use the native browser cache
			            // this requires a good expires header on the server
			            document.cookie = _fileArray[0];
		 
			            // if this isn't an old browser
			        } else {
			            // use the cached version if we already have it
						//console.log( fileIsCached(_fileArray) );
			            if ( fileIsCached(_fileArray) ) {
			                injectRawStyle(sessionStorage.getItem(_fileArray[0]), _fileArray[0]);
			                // otherwise, load it with ajax
			            } else {
			                var xhr = new XMLHttpRequest();
			                xhr.open("GET", _fileArray[1], true);
			                on(xhr, 'load', function () {
			                    if ( xhr.readyState === 4 ) {
			                        // once we have the content, quickly inject the css rules
			                        injectRawStyle(xhr.responseText, _fileArray[0]);
			                        // and cache the text content for further use
			                        // notice that this overwrites anything that might have already been previously cached
			                        sessionStorage.setItem(_fileArray[0], xhr.responseText);
			                        //sessionStorage.setItem(_fileArray[0] + '_file', _fileArray[1]);
			                    }
			                });
			                xhr.send();
			            }
			        }
			    }
		 
			    // this is the simple utitily that injects the cached or loaded css text
			    function injectRawStyle(text, id) {
				    if( document.getElementById(id) ){
					    document.getElementById(id).innerHTML = text;
				    }else {
					    var style = document.createElement('style');
					    style.innerHTML = text;
					    document.getElementsByTagName('head')[0].appendChild(style);
				    }
			    }
		 
			}());

cache.min.js

var css_href_array=[];(function(){"use strict";function t(){var e=navigator.userAgent.toLowerCase();if(e.indexOf("msie")!=-1&&parseInt(e.split("msie")[1])==8){return"ie8"}else{return"default"}}function r(e,t,n){if(e.addEventListener){e.addEventListener(t,n,false)}else if(e.attachEvent){e.attachEvent("on"+t,n)}}function s(e){return window.sessionStorage&&sessionStorage.getItem(e[0])}function o(e){if(!window.sessionStorage||!window.XMLHttpRequest){var t=document.createElement("link");t.href=e[1];t.rel="stylesheet";t.type="text/css";document.getElementsByTagName("head")[0].appendChild(t);document.cookie=e[0]}else{if(s(e)){u(sessionStorage.getItem(e[0]),e[0])}else{var n=new XMLHttpRequest;n.open("GET",e[1],true);r(n,"load",function(){if(n.readyState===4){u(n.responseText,e[0]);sessionStorage.setItem(e[0],n.responseText)}});n.send()}}}function u(e,t){if(document.getElementById(t)){document.getElementById(t).innerHTML=e}else{var n=document.createElement("style");n.innerHTML=e;document.getElementsByTagName("head")[0].appendChild(n)}}var e=document.getElementsByClassName("js-style");for(var n=0;n<e.length;n++){if(e[n].getAttribute("data-font")){css_href_array.push([e[n].getAttribute("id"),e[n].getAttribute("data-href")+t()+".css"])}else{css_href_array.push([e[n].getAttribute("id"),e[n].getAttribute("data-href")])}}for(var i in css_href_array){if(window.sessionStorage&&sessionStorage.getItem(css_href_array[i][0])||document.cookie.indexOf(css_href_array[i][0])>-1){o(css_href_array[i])}else{r(window,"load",o(css_href_array[i]))}}})()