Отправить GET или POST запросом base64 из Javascript в PHP?

function createDownloadLink(blob, encoding) {
    var reader = new FileReader();
    reader.readAsDataURL(blob)
    reader.onloadend = function () {
        var base64data = reader.result;


        var data = null;
        var xhr = new XMLHttpRequest();
        xhr.withCredentials = true;

        var param = base64data.slice(base64data.indexOf(',') + 1);

        console.log(param);
        xhr.open("GET", "search3.php?action="+param);
        xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
        xhr.send(null);

        xhr.addEventListener("readystatechange", function () {
            if (this.readyState === 4) {
                console.log(this.responseText);
            }
        });

        //document.getElementById('pppp').textContent=url;
    }
}