loadFile

(function() {
    'use strict';

    function getType(src) {
        return src.match(/\.([^\.\?]+)(?:\?.*)?$/)[1];
    }

    function injectContent(content, type) {
        if (type === 'css') {
            var style = document.createElement('style');

            document.head.appendChild(style);
            style.textContent = content;
        } else {
            document.head.insertAdjacentHTML('beforeend', content);
        }
    }

    window.loadFile = function(src) {
        if (!window.localStorage || !window.addEventListener) {
            return false;
        }

        var content = localStorage[src];

        if (content) {
            injectContent(content, getType(src));
        } else {
            var xhr = new XMLHttpRequest();

            xhr.addEventListener('load', function() {
                localStorage[src] = xhr.responseText;
                injectContent(xhr.responseText, getType(src));
            });

            xhr.open('GET', src);
            xhr.send();
        }
    };

})();