function request(uri, callback, params) {
var i = new XMLHttpRequest();
i.open('POST', uri, true);
i.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
i.send(params);
i.onload = function() {
callback(this.status == 204 ? 'Success' : this.responseText);
};
return i;
}