XMLHttpRequest problem z pętlą "for"

function loadDoc(x) {	
  var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {    
      document.getElementById("demo"+x).innerHTML = this.responseText + x + "<br>"; 	   
    }
  };
  xhttp.open("GET", "ajax_info.txt", true);
  xhttp.send();
}

function mojafunkcja() {
	for (i=0; i<256; i++) {		
		loadDoc (i);
	}
	//Dalszy kod przetwarza dane zebrane przez kod
}

        function loadDoc(x) {
            return new Promise(function (resolve, reject) {
                var xhttp = new XMLHttpRequest();
                xhttp.onreadystatechange = function () {
                    if(this.readyState !== 4) return;

                    if (this.status == 200) {
                        resolve(this.responseText);
                    } else {
                        reject();
                    }
                };
                xhttp.open("GET", "ajax_info.txt", true);
                xhttp.send();
            });
        }

        function loadAllDocs(x) {
            if(x < 256) {
                loadDoc(x).then(function(response) {
                    // do something with response
                    loadAllDocs(++x);
                });
            }
        }

        loadAllDocs(0);