Khan Academy API JS Wrapper

khan.js

var khan = (function (document) {
    var _head = document.getElementsByTagName('head')[0],
        _reusable_script_ele = document.createElement('script'),
        _default_host = 'http://www.khanacademy.org/api/v1/';
    
    var _jsonp = function (url) {
        var script = _reusable_script_ele.cloneNode(false);
        script.src = url;
        _head.appendChild(script);
    };
    
    var _api = function (endpoint, callback) {
        var url = _default_host + endpoint.replace(/^\/+/, '') + '?callback=khan.callback';
        _callback = callback;
        _jsonp(url);
    };
    
    return {
        api: _api,
        callback: function (res) {
            _callback(res);            
        }
    };
}(document));