jQuery AJAX polling for JSON response, handling based on AJAX result or JSON content

You could use a simple timeout to recursively call ajax_request.

success: function(xhr_data) {
  console.log(xhr_data);
  if (xhr_data.status == 'pending') {
    setTimeout(function() { ajax_request(); }, 15000); // wait 15 seconds than call ajax request again
  } else {
    success(xhr_data);
  }
}

Stick a counter check around that line and you’ve got a max number of polls.

if (xhr_data.status == 'pending') {
  if (cnt < 6) {
    cnt++;
    setTimeout(function() { ajax_request(); }, 15000); // wait 15 seconds than call ajax request again
  }
}

You don’t need to do anything in your error function unless you want to put an alert up or something. the simple fact that it error will prevent the success function from being called and possibly triggering another poll.