Question

I am trying call an ajax request until it returns a true value. I have tried the following code but it does not return any results and no errors in the console. Any idea what I am doing wrong?

function getUserData() {
var xhr = new XMLHttpRequest();
xhr.open("GET", "http://api.example.com/data.json", true);
xhr.onreadystatechange = function() {
  if (xhr.readyState == 4) {
    var resp = JSON.parse(xhr.responseText);
    return resp.status;
  }
}
xhr.send();
}

setInterval(function () {
if (getUserData() === "true") {
   alert("true");
}
}, 10000);

Answer 1

getUserData calls an asynchronous function internally, so it has returned long before the AJAX call is actually finished.

Instead of doing this in a setInterval loop, you might want to try calling getUserData again in the failure case. For example:

function getUserData() {
    var xhr = new XMLHttpRequest();

    xhr.open("GET", "http://api.example.com/data.json", true);
    xhr.onreadystatechange = function() {
        if (xhr.readyState == 4) {
            var resp = JSON.parse(xhr.responseText);
            if (resp.status) {
                alert("true");
            } else {
                setTimeout(getUserData, 10000);
            }
        }
    }
    xhr.send();
}

getUserData();