request.js

    function (opts, data, method, headers) {
        if (_.isString(opts))
            opts = { url: opts };

        opts = _.defaults(opts, {
            method: method || 'GET',
            data: data || null,
            header: headers || {},
            statusFilter: function (status) {
                return status < 300;
            }
        });

        var req = new XMLHttpRequest();

        var promise = new Promise(function (resolve, reject) {
            req.addEventListener('readystatechange', function () {
                if (req.readyState === 4) {
                    if (req.status === 0)
                        return reject(new Error('request abort by browser'));

                    if (opts.statusFilter(req.status)) {
                        reject(req);
                    } else {
                        req.json = function () { JSON.parse(req.responseText) };
                        resolve(req);
                    }
                }
            });

            req.open(opts.method, opts.url);

            _.map(
                opts.headers,
                _.rearg(req.setRequestHeader.bind(req), [1, 0])
            );

            req.send(opts.data);
        })

        promise.req = req;
        return promise;
    }