retrieving data from db dynamic doesn't work

I have my data in mysql. I am using PDO to pull data with php then using json_encode to convert to js. When i use following scenario, i always get output NaN and if i use static array it works. So I am guessing it's either wrong json format or something with php.

This works if I set values for array smoothly: codepen: http://codepen.io/pghiran/pen/QEvRjW

Dynamic (pulling data from db and storing in array, doesn't work. My code for doing this:

PHP

$exchangeRates =  array();

$sql = 'SELECT * FROM exchange';

try {
    $stmt = $conn->prepare($sql);
    $stmt->execute();

    for ($i=0; $row=$stmt->fetch();$i++){
        $exchangeRates[] = array($row['rs3'],$row['07'],$row['deadman'],$row['currency']);
    }
}catch(exception $e){
    return $e;
}

var_dump($exchangeRates);

var_dump displays: array(1) { [0]=> array(4) { [0]=> string(3) "0.5" [1]=> string(3) "1.5" [2]=> string(3) "3.5" [3]=> string(1) "$" } }

JS/Jquery:

var amount = $('#amount'),
                    goldtype = $('#goldtype'),
                    exchange= <?php echo json_encode($exchangeRates);?>,
                    price = $('#price');

                    console.log(exchange); 

                    goldtype.change(function () {
                        var exchangeIndex = $("select[name='goldtype'] option:selected").index();
                        price.val(amount.val() * exchange[exchangeIndex]);
                    })

console.log(exchange) displays:

[Array[4]]
0
:
Array[4]
0
:
"0.5"
1
:
"1.5"
2
:
"3.5"
3
:
"$"
length
:
4

https://gyazo.com/b167b38d62d9c4b567f31cc35ce00289