Sharepoint Modern Update listItem

Update list in a modern site, getting formDigestValue

console.clear();
var dataToManage = {};
function getItemTypeForListName(listTitle, returnfct){
	var xhr = new XMLHttpRequest();
	var url = _spPageContextInfo.webAbsoluteUrl;
	if (url === "undefined") {
		console.log("_spPageContextInfo.webAbsoluteUrl undefined");
		url = "http://siteUrl";
	}
	
	xhr.open('GET', url + "/_api/web/lists/getbytitle('" + listTitle + "')/?$select=ListItemEntityTypeFullName");
	xhr.setRequestHeader("Accept", "application/json; odata=verbose");
	xhr.onload = function () {
		if (xhr.status === 200) {
			var kk = JSON.parse(xhr.responseText);
			console.dir(kk.d.ListItemEntityTypeFullName);
                        var returnValue = {};
			returnValue.ListItemEntityTypeFullName = kk.d.ListItemEntityTypeFullName;
			if(returnfct != null)
				returnfct(returnValue);
		}
		else {
			console.dir(xhr);
			alert('Request failed.  Returned status of ' + xhr.status);
		}
	};
	xhr.send();
}

//get FormDigestValue to do POST requests
function GetDisgestValue(returnFct){
    var url = _spPageContextInfo.webAbsoluteUrl + "/_api/contextinfo";
	var xhr = new XMLHttpRequest();
	xhr.open('POST', url, true);
	xhr.setRequestHeader("Accept", "application/json; odata=verbose");
	xhr.setRequestHeader("content-type", "application/json; odata=verbose");
	xhr.onload = function (data) {
		if (xhr.status === 200) {
			console.log("success");
			var d = JSON.parse(xhr.responseText);
			console.dir(d.d.GetContextWebInformation.FormDigestValue);
			dataToManage.FormDigestValue = d.d.GetContextWebInformation.FormDigestValue;
			returnFct(d.d.GetContextWebInformation.FormDigestValue);
		}
		else {
			console.log("error");
			console.log(xhr.status);
			console.dir(xhr);
			console.dir(xhr.responseText);			
		}
	};
	xhr.send();
}

function UpdateListItem(){
	
    var url = _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getbytitle" + 
	"('" + dataToManage.listName + "')/items("+dataToManage.itemId+")";
	
	var xhr = new XMLHttpRequest();
	xhr.open('POST', url, true);
	xhr.setRequestHeader("Accept", "application/json; odata=verbose");
	xhr.setRequestHeader("X-RequestDigest", dataToManage.FormDigestValue );
	xhr.setRequestHeader("content-type", "application/json; odata=verbose");
	xhr.setRequestHeader("X-HTTP-Method", "MERGE");
	xhr.setRequestHeader("If-Match", "*");
	
	xhr.onload = function () {
		if (xhr.status === 204) {
			console.log("success");
		}
		else {
			console.log("error");
			console.log(xhr.status);
			console.dir(xhr);
			console.dir(xhr.responseText);
			
		}
	};
	var str = JSON.stringify(dataToManage.item);
	xhr.send(str);
} 

function withDigestValue(formDigestValue){
	console.log("formDigestValue : " + formDigestValue);	
}

function getListDatas(data){
	console.log(data.ListItemEntityTypeFullName);
	dataToManage.listName = "aTest";//list title to update
	dataToManage.itemId = 1;//id of the item to update
	dataToManage.item = {
        "__metadata": { "type": data.ListItemEntityTypeFullName },
		"Title": "new title"//new fields values
    };
	GetDisgestValue(UpdateListItem);
}

getItemTypeForListName("atest", getListDatas);