How do I access this variable in Google maps API?

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Javascript

PHP

Ajax

Google-Maps

I have a google maps web application for a game where the user will click a google map marker, make a selection in the window that pops up and click submit. It uses AJAX to update the database with information selected by the user. The database is pre-populated with names of the markers and GPS coordinates, which are loaded. The markers are also placed accordingly upon load via XML.

I'm having trouble updating one row in my DB called quest with the user selected information when it's submitted. Currently, a user can select a marker and submit a quest, but it won't update the DB at all.

This is what happens when the submit button is pressed

if (document.getElementById("questType").value == 
"quest1") { //if quest1 is selected upon submission
alert("quest1");
var markerName;
var questName = "Quest 1";
xmlhttp = new XMLHttpRequest();        
xmlhttp.open("GET", "ajax.php?questName=" + questName + "&markerName=" + markerName, true);         
xmlhttp.send(); //Sending the request to the server

Here's my ajax.php

<?php 
include("connect.php");
require("call2.php");
$markerName = mysqli_real_escape_string($con, $_GET['markerName']);
$questName = mysqli_real_escape_string($con, $_GET['questName']);


$stmt = $con->prepare("UPDATE markers SET quest = $questName WHERE markerName = $markerName");
$stmt->bind_param($questName, $markerName);
$stmt->execute();
$stmt->close();
?>

Here's my call file as well

$dom     = new DOMDocument("1.0");
$node    = $dom->createElement("markers");
$parnode = $dom->appendChild($node);
include('connect.php');
$query  = "SELECT * FROM markers WHERE 1"; // Select all the rows in the markers table
$result = mysqli_query($con, $query);
if (!$result) {
die('Invalid query: ' . mysqli_error($con));
}

// Iterate through the rows, adding XML nodes for each
while ($row = mysqli_fetch_assoc($result)) {
global $dom, $node, $parnode;

$node    = $dom->createElement("marker");
$newnode = $parnode->appendChild($node);
$newnode->setAttribute("markerName", 
$row['markerName']);
$newnode->setAttribute("quest", $row['quest']);
$newnode->setAttribute("lat", $row['lat']);
$newnode->setAttribute("longg", $row['longg']);
}

header("Content-type: text/xml");
echo $dom->saveXML();

Sorry if this is a lot, I think the problem is i'm not assigning a value to markerName. I don't get any errors, however when I hover over the ajaxphp in the network tab on chrome it looks like it's getting the questName but markerName remains undefined.

Here's where I'm loading things in

downloadUrl("call2.php", function(data) {
var xml = data.responseXML;
var markers = xml.documentElement.getElementsByTagName("marker");
for (var i = 0; i < markers.length; i++) {
var name = markers[i].getAttribute("markerName"); //<------ here's where it's getting markerName
//  var address = markers[i].getAttribute("address");
var type = markers[i].getAttribute("type");
var point = new google.maps.LatLng(
  parseFloat(markers[i].getAttribute("lat")),
  parseFloat(markers[i].getAttribute("longg")));
var icon = customLabel[type] || {};
var marker = new google.maps.Marker({
map: map,
position: point,
icon: icon.icon,
shadow: icon.shadow
  });
  bindInfoWindow(marker, map, infoWindow, html);
}
});

I think I need to figure out a way to access name, but I'm unsure how to when it's local to the function which downloads the XML file.

What I have tried:

Debugging using chrome, using netbeans