XHR using ES6 Promise

es6_xhr.js

var xhr = function(x, y, z) {
    var a;
    return new Promise(function(o, p) {
        with(a = new XMLHttpRequest) open(y || "GET", x), send(z || null), onload = function(n) {
            o(n.target.responseText)
        }, onerror = p
    })
};

//usage:
// GET - xhr('http://www.mysite.com/api/etc').then(function(data) { console.log(data) });
// POST - xhr('http://www.mysite.com/api/etc', 'POST', {hello:1}).then(function(data){ console.log(data) });