Receive array from php to javascript

Question

This is probably something simple but i can't figure out the solution. I have a Javascript that ask for some data from a PHP. Data included in an array. I am actually receiving the array from php but i can't fragmented it.

this is the PHP file:

<?php

$q1 = intval($_REQUEST["qq1"]);

// some data
// $reply_1 = "daTa1";
// $reply_2 = "data2";
// $reply_3 = "987654321";
//..............

$arr = array(
$reply_1,
$reply_2,
$reply_3,
$reply_4);

echo json_encode($arr);
?>

and the below is part of the javascript

var datareceived= new Array (15);

var url = "theabovePHP.php?qq1="+i;

function reqListener () {
     console.log(this.responseText);
              }

     var oReq = new XMLHttpRequest(); 
    oReq.onload = function() {
      datareceived= this.responseText;
    }

    oReq.open("get", url, false); // false wait
    oReq.send();

document.getElementById('div_display_part_OF_data').innerHTML = datareceived[1]+" some data " + datareceived[2];

The issue is that i am receiving the data in var datareceived, that looks like this ["daTa1","data2","987654321","2015/09/27 16:20:48","35.1320112","33.344586"] but I can't have them as an array. When I ask the datareceived[3], this should be 987654321, i receive "T" (the 3rd charachter in datareceived) etc..