How to pass FormData over XMLHttpRequest using GET method

When Method of the senderform is POST, everything works fine. However, as soon as I change the method to GET, I don't receive anything on the server.

function ajaxSubmit(destinationElement, senderform) {

    var xmlreq = new XMLHttpRequest();
    var params = new FormData(senderform);
    xmlreq.open(senderform.method, senderform.action, true);

    if (/\/content\.php$/.test(senderform.action))
        xmlreq.onreadystatechange = receiveTable;
    else xmlreq.onreadystatechange = receiveText;

    xmlreq.send(params);
}

I know that I could manually append key-value pairs at the end of Action address, but the problem is that I don't know which form is going to be passed with what fields.

I would prefer native javaScript if possible.

How can I send a GET request using XMLHttpRequest with key-value pairs from senderform which points to form Element (the same way as it already works for POST requests)?