var MYAPP = MYAPP || {};

MYAPP.ajax = function(url, callback, method, data, async){
    var _url = typeof(url) === 'string' ? url : null,
    _callback = typeof(callback) === 'function' ? callback : function(){},
    _method = ['GET','HEAD','POST','DELETE','PUT'].contains(method) ? method : 'GET',
    _data = typeof(data) === 'string' ? data : null,
    _async =  typeof(async) === 'boolean' ? async : true,
    xmlHttp = null;

    if (window.XMLHttpRequest) {
        xmlHttp = new XMLHttpRequest();
    } else if (window.ActiveXObject) {
        try {
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
        } catch(e) {
            try {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            } catch(e) {
                xmlHttp = null;
            }
        }
    } else if (window.createRequest) {
        try {
            xmlHttp = window.createRequest();
        } catch (e) {
            xmlHttp = null
        }
    };

    if(xmlHttp && _url){
        xmlHttp.open(_method, _url, _async);
        xmlHttp.onreadystatechange = function() {
            if (this.readyState === 4) {               
                    _callback(this.responseText, this.status);           
            }
        };
        if(_method === 'POST'){
            xmlHttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
            xmlHttp.setRequestHeader('Content-length', _data ? _data.length : 0);
            xmlHttp.setRequestHeader('Connection', 'close');
        }
        xmlHttp.send(data);
    }
};

MYAPP.ajax('http://fake.url',
            function(data, status){
                if(status === 200) {
                       console.log(data);
                }
            });