simple-ajax.js

function ajax(url, cb, errcb) {
    var xhr;
    xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.onreadystatechange = function () {
        if (4 === xhr.readyState) {
            if(xhr.status >= 200 && xhr.status < 400){
                cb(xhr);
            } else {
                errcb(xhr);
            }
        }
    };
    xhr.send();
}