How to reads JSON data from a web server running PHP and MySQL?

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Javascript

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JSON

I try to reads JSON data from a web server running PHP and MySQL.
I learn code from http://www.w3schools.com/json/json_example.asp
And then I I changed their url with my urlm like this http://localhost/demo.php
But it does not work. I am beginner in JSON and I don't know what happened with my code. Please help me, thank.
Here is my PHP code:

<?php
$servername = "localhost";
$username = "root";
$password = "";
// Create connection
$conn = new mysqli($servername,$username,$password);
//check connection
if ($conn->connect_error) 
{
    die("Connection failed: " . $conn->connect_error);
}
$db_selected = mysqli_select_db($conn,"test_json");
if(!$db_selected)
{
	die("Không thể sử dụng DATABASE: ".mysql_error());
}
$sql = "SELECT * from data";
$result = $conn -> query($sql);
$outp = "[";
while($rs = $result->fetch_array(MYSQLI_ASSOC)) {
    if ($outp != "[") {$outp .= ",";}
    $outp.='{"Name":"'.$rs["Name"].'",';
    $outp.='"Age":"'.$rs["Age"].'",';
    $outp.='"Address":"'.$rs["Address"].'",';
	$outp.='"Phone":"'.$rs["Phone"].'"}';
}
$outp.="]";
$conn->close();
echo($outp);
?>

And here is my JSON

<h1>Customers</h1>
<div id="id01"></div>

<script>
var xmlhttp = new XMLHttpRequest();
var url = "http://localhost:80/demo.php";


xmlhttp.onreadystatechange=function() 
{
    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
        myFunction(xmlhttp.responseText);
    }
}
xmlhttp.open("GET", url, true);
xmlhttp.send();

function myFunction(response) {
    var arr = JSON.parse(response);
    var i;
    var out ="<table>";

    for(i = 0; i < arr.length; i++) {
        out +="<tr><td>" +
        arr[i].Name +
        "</td><td>" +
        arr[i].Age +
        "</td><td>" +
        arr[i].Address +
        "</td><td>"+
		arr[i].Phone +
        "</td></tr>";
    }
    out+="</table>"
    document.getElementById("id01").innerHTML = out;
}
</script>