Simple $.ajax to XMLHttpRequest

ajax2xmlhttprequest.js

jQuery.ajax = function(opts) {
    var xhr = new XMLHttpRequest({mozSystem: true});
    var method = opts.type || 'GET';
    method = method.toUpperCase();
    if ('POST' !== method && opts.data) {
        opts.url += '?' + jQuery.param(opts.data);
    }
    xhr.open(method.toUpperCase(), opts.url);
    xhr.responseType = opts.dataType || 'json';
    xhr.onreadystatechange = function () {
        if (xhr.status === 200 && xhr.readyState === 4) {
            opts.success(xhr.response);
        }
    }
    xhr.onerror = function () {
        opts.error(xhr, 'error');
    };
    if ('POST' === method && opts.data) {
        xhr.send(JSON.stringify(opts.data));
    } else {
        xhr.send();
    }
}