JSON data retrival

<!DOCTYPE html>
<html>
<body>

<div id="json"></div>

<script>
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
        var arr = JSON.parse(xmlhttp.responseText);
        for(var i = 0; i < arr.length; i++)
           document.getElementById("json").innerHTML +=  '<p>' + arr[i].sub  + ' by '+ arr[i].teacher;
    }
}
xmlhttp.open("GET", "mySubjects.txt", true);
xmlhttp.send();
</script>
<pre>
[{"sub": "Advanced Inernet Technology","teacher": "Prof. Sanober"},
{"sub": "Disrubuted Systems","teacher": "Prof. Bhushan"},
{"sub": "Software Engg","teacher": "Prof. Madhuri"},
{"sub": "Data Mining","teacher": "Prof. Shanti"}]
</pre>
</body>
</html>