Json.parse: unexpected non-whitespace character?

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PHP

Ajax

jQuery

HTML5

Hello friends,
I face to this problem please help me, the array which I return from php file I can not access its element in my ajax code, can you help me plz,
its my php code

<?php
require_once("connection.php");
global $conn;

if (isset($_POST['expGoodsName'])) {

$expCheckSNo=$_POST['expCheckSNo'];
$goodsName=$_POST['expGoodsName'];

$goodsNamequery= mysqli_query($conn,"SELECT S.Quantity, S.Unit, S.UnitPrice FROM tblstock S
INNER JOIN tblimportcheck imp USING(ImpSNo)
INNER JOIN tblexportcheck exp USING(ImpSNo)
WHERE exp.ExpSNO =$expCheckSNo AND S.GoodsName='$goodsName' ");

$rows=mysqli_fetch_assoc($goodsNamequery);

$qty=$rows['Quantity'];
$Unit=$rows['Unit'];
$UnitPrice=$rows['UnitPrice'];

$myArr = array($qty,$Unit, $UnitPrice);

$myJSON = json_encode($myArr);

echo $myJSON;

}
?>


here is ajax code:
$("#expGoodsName").change(function getQuantity(argument) {
sendImportCheck();
});

function sendImportCheck()
{
var XMLHttp;
if (window.XMLHttpRequest) {
// code for modern browsers
XMLHttp = new XMLHttpRequest();
}else {
// code for old IE browsers
XMLHttp = new ActiveXObject("Microsoft.XMLHTTP");
}

var expCheckSNo=$("#expCheckSNo").val();
var expGoodsName=$("#expGoodsName").val();

XMLHttp.onreadystatechange=function()
{
if(XMLHttp.status==200 && XMLHttp.readyState==4) {

var myresult= JSON.parse(XMLHttp.responseText);
alert(myresult[0]);//it should display first element

}
}
XMLHttp.open("POST","ExpCheckEdit.php",true);
XMLHttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
XMLHttp.send("expCheckSNo="+expCheckSNo+"&expGoodsName="+expGoodsName);
}

What I have tried:

I tried a lot in google but nothing changed