I've got the ajax request is very slow so my stats array does not get updated at the second time i want to access it. It seems like the ajax request gets executed after all the code is processed. Is there a way how i can wait for the ajax request to be executed before all the rest of my code?

console.log(stats);
fetchREST(false, (url+selectedID+"/solve"), (parseInt(button.id)+1), function(data){
 if (data.success) {
  console.log("richtig");
  stats.right++;
 } else {
  console.log("falsch");
  stats.wrong++;
 }
});
console.log(stats);

function fetchREST(isGET, path, answer, callback) {
    var httpRequest = new XMLHttpRequest();
    httpRequest.onreadystatechange = function() {
        if (httpRequest.readyState === 4) {
            if (httpRequest.status === 200) {
                var data = JSON.parse(httpRequest.responseText);
                if (callback) callback(data);
            }
        }
    };

    let email = "*";
    let pw = "*";

    if(isGET) {
        // not needed
    } else {
        let solutionArray = '[' +  answer +  ']';
        console.log(solutionArray);
        httpRequest.open('POST', path, true);
        httpRequest.setRequestHeader("Content-Type", "application/json");
        httpRequest.setRequestHeader("Access-Control-Allow-Origin", "*"); 
        httpRequest.setRequestHeader("Access-Control-Allow-Headers", "*");
        httpRequest.setRequestHeader("Authorization", "Basic " + window.btoa(email + ":" + pw));
        httpRequest.send(solutionArray);
    }
}

EDIT I fixed it by changing

httpRequest.open('POST', path, true);

to

httpRequest.open('POST', path, false);

Now the async is set to false and the send methods waits until a response is received.