JavaScript: Async js/css file loader

load.js

function load (arr, suc, err) {
    var libs = [];
    for (var i = 0, len = arr.length; i < len; i++) {
        var el = arr[i];
        // var domElem = null;
        var extension = el.split(".")[el.split(".").length - 1];
        switch (extension) {
            case "css":
                (function() {
                    $("<link/>", {
                        rel: "stylesheet",
                        type: "text/css",
                        href: el
                    }).appendTo("head");
                })();
                break;
            case "js":
                (function() {
                    if (!suc) {
                        $("<script/>", {
                            type: "text/javascript",
                            src: el
                        }).appendTo("head");
                    } else {
                        libs.push(el);
                    }
                })();
                break;
            default:
                console.warn("file not found: ", el);
        }
    }
    // synched version with callback                        
    if (libs.length > 0) {
        $.when.apply(this, libs.map(function(src) {
            return $.getScript(src);
        })).done(suc).fail(err);
    }
}