function sendRequest(method, url, callback, data)
{
    let request = new XMLHttpRequest();

    request.onreadystatechange = function() {
        if (request.readyState === XMLHttpRequest.DONE) {
            let response = {
                status : request.status,
                headers : request.getAllResponseHeaders(),
                contentType : request.responseType,
                content : request.response
            };

            callback(response);
        }
    }

    request.open(method, url);

    if (data) {
        // TODO: understand these headers
        request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        request.setRequestHeader("Content-length", data.length);
        request.setRequestHeader("Connection", "close");
        request.send(data);
    } else {
        request.send();
    }
}