Abusing localStorage to build an aggressive cache

gistfile1.js

var assets = [
    'http://localhost/offline-assets/fancybox/jquery.fancybox-1.3.4.js',
    'http://localhost/offline-assets/fancybox/jquery.fancybox-1.3.4.css'
];

for (var i=0,l=assets.length; i<l; i++) {
    loadAsset(assets[i]);
}

function loadAsset(url){
    var asset = getCache(url);
    if (asset.mimetype == 'text/css') {
        var style = document.createElement('style');
        style.type = asset.mimetype;
        style.innerHTML = asset.data;
        document.getElementsByTagName('head')[0].appendChild(style);
    } else if (asset.mimetype == 'text/javascript') {
        eval(asset.data);
    }
}

function getCache(url) {
    if (localStorage[url]) {
        //in cache
        return JSON.parse(localStorage[url]);
    } else {
        //not in cache, sync load
        var data = '';
        var asset = {};
        $.ajax({
            'async' : false,
            'url' : url,
            'success' : function(data, status, xhr) {
                var header = xhr.getResponseHeader('Content-type');
                var mimetype = 'text/plain';
                if (header.indexOf('javascript') !== -1) {
                    mimetype = 'text/javascript';
                } else if (header.indexOf('css') !== -1) {
                    mimetype = 'text/css';
                }

                asset = {
                    'mimetype' : mimetype,
                    'data' : data
                }
                localStorage[url] = JSON.stringify(asset);
            }
        });
        return asset;
    }
}

I know, sync load is stupid for performance.