JSON.parse(xmlhttp.responseText) unexpected character - php

Question

I keep getting an unexpected character error in the console for the line
var a = JSON.parse(xmlhttp.responseText);
and I'm not sure why. Could this be why my textboxes aren't populating with the parsed data?
Main page code:
function loadDoc()
{
var xmlhttp;
// code for IE7+, Firefox, Chrome, Opera, Safari
if (window.XMLHttpRequest)
{
xmlhttp=new XMLHttpRequest();
}
// code for IE6, IE5
else
{
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
var doc = window.document.createElement("doc");
var a = JSON.parse(xmlhttp.responseText);
document.getElementById("textbox").innerHTML=a.first;
document.getElementById("textbox2").innerHTML=a.second;
}
}
xmlhttp.open("GET","loadTextBox.php?id=4",true);
xmlhttp.send();
}
loadTextBox.php code:
<?php
---Placeholder for correct DB login info---
$result = $mysql->query(---Placeholder for correct SQL query---);
while ($row = $result->fetch_object())
{
$queryResult[] = $row->present_tense;
}
$textboxValue = $queryResult[0];
$textboxValue2 = $queryResult[2];
echo json_encode(array('first'=>$textboxValue,'second'=>$textboxValue2));
?>

Answer 1

Your loadTextBox.php file should not contain any HTML because the JSON.parse method expects only JSON:
<?php
header("Content-type: application/json");
$db_username = placeholder;
$db_password = placeholder;
$db_host = placeholder;
$result = $mysql->query(---Placeholder for correct SQL query---);
while ($row = $result->fetch_object())
{
$queryResult[] = $row->present_tense;
}
$textboxValue = $queryResult[0];
$textboxValue2 = $queryResult[2];
echo json_encode(array('first'=>$textboxValue,'second'=>$textboxValue2));
?>
If your DB login info is in a separate file, then there should be no HTML or BODY tags only the PHP tags.