HTML5 Boilerplate-friendly CORE JS Lib Loader: An improvement on my 'jQuery Lib Loader'. It doesn't rely on jQuery. It can pull in assets at will and be used anywhere in the body.

lib_loader_js

var Ajax = function (url, callback, where) {
    "use strict";
    var _this = this;
    _this.httpRequest = false;
    _this.callback = callback;
    _this.where = where;
    _this.url = url;
    _this.init();
};
Ajax.prototype = {
    init: function () {
        "use strict";
        //console.log('initiated');
        var _this = this;
        if (window.XMLHttpRequest) {
            _this.httpRequest = new XMLHttpRequest();
        } else if (window.ActiveXObject) {
            _this.httpRequest = new window.ActiveXObject("Microsoft.XMLHTTP");
        }
        _this.resp();
    },
    resp: function () {
        "use strict";
        var _this = this;
        _this.httpRequest.onreadystatechange = function () {
            if (_this.httpRequest.readyState === 4) {
                if (_this.httpRequest.status === 200) {
                    var testJSON = _this.httpRequest.response.indexOf("{") === 0;
                    if (testJSON) {
                        new _this.JSONCallback(_this.httpRequest.response);
                    } else {
                        var script = document.createElement("script");
                        script.src = _this.url;
                        document.getElementsByTagName("head")[0].appendChild(script);
                        if (_this.callback) {
                            _this.callback();
                        }
                    }
                } else {
                    alert("There was a problem with the request.");
                }
                //Remove the above alert, as it's only for testing purposes.
            }
        };
    },
    JSONCallback: function (data) {
        "use strict";
        var _this = this;
        //console.log("JSON detected...");
        //Remove the console call for browser compatibility, if using in a production environment.
        if (_this.callback) {
            _this.callback(data);
        }
    },
    call: function () {
        "use strict";
        var _this = this;
        _this.httpRequest.open("GET", _this.url, true);
        _this.httpRequest.send(null);
    }
};
var libLoader = {};
libLoader.init = function (lib_type, callback) {
    "use strict";
    function renderScript() {
        var ajaxy = new Ajax(lib_type, callback);
        ajaxy.call();
    }
    if (lib_type !== "undefined") {
        renderScript();
    }
};