CanvasJS: Making a chart dynamic with data.php, json encode and ajax(bandwidth meters)

First things first, I am trying to parse the data from a data.php file that uses json encode to echo a datapoint. The datapoint is updated every time the data.php file is requested, but not in a series of datapoints. Instead it just changes the time value and refreshes its y content. I haven't found a working way to actually make the php file echo series of datapoints and not update a single one.

Next up, the chart parses the data.php file and it indeed shows the datapoint. BUT I want to make this chart update every second and add new datapoints on every update so that I have a working bandwidth graph.

Here is my code:

index.php:

<!DOCTYPE HTML>
<html>
<head>  
<script type="text/javascript" src="canvasjs.min.js"></script>
  <script type="text/javascript" src="js/jquery-2.1.4.min.js"></script>
    <script>
$(document).ready(function () {
$.getJSON("data.php", function (data_points) {
    var dps = data_points
var chart = new CanvasJS.Chart("chartContainer", {
zoomEnabled: true,
panEnabled: true,
animateEnabled: true,
data: [ {
type: "splineArea",
xValueType: "label",
y: "y",
dataPoints: dps } ]
});
chart.render();
});
});
</script>
</head>
<body>
    <div id="chartContainer" style="height: 300px; width: 100%;">
    </div>
</body>
</html>

data.php:

<?

session_start();
session_destroy();
session_start();

$rx[] = @file_get_contents("/sys/class/net/wlan0/statistics/rx_bytes");
sleep(1);
$rx[] = @file_get_contents("/sys/class/net/wlan0/statistics/rx_bytes");

$rbps = $rx[1] - $rx[0];

$round_rx=round($rbps/1, 2);

$time=date("Y-m-d H:i:s");
$_SESSION['rx'] = $round_rx;
$data_points['label'] = $time;
$data_points['y'] = $_SESSION['rx'];

echo json_encode([$data_points]);

?>

If anyone know on how to make this map dynamic then please provide me some help. An example output of the data.php file (what it echoes) is the following:

[{"label":"2015-09-12 21:34:12","y":1500}]

Thank you in advance for any help provided.

Solution

In order to update charts that way, you need to create chart only once (outside the ajax request) and keep adding new dataPoints via ajax request each second as shown below.

<!DOCTYPE HTML>
<html>
    <head>  
        <script type="text/javascript" src="canvasjs.min.js"></script>
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
        <script>
            $(document).ready(function () {
                var chart = new CanvasJS.Chart("chartContainer", {

                    zoomEnabled: true,
                    panEnabled: true,
                    animateEnabled: true,
                    data: [ {
                        type: "splineArea",
                        xValueType: "label",
                        y: "y",
                        dataPoints: [] 
                    } ] 

                });

                function updateChart(){
                    $.getJSON("data.php", function (data_points) {
                        for(var i = 0; i < data_points.length; i++){
                            chart.options.data[0].dataPoints.push(data_points[i]);
                        }

                        chart.render();
                    });
                }               

                var updateInterval = 1000;

                setInterval(function(){
                        updateChart()
                }, updateInterval);

            });

        </script>
    </head>
    <body>
        <div id="chartContainer" style="height: 300px; width: 500px;"></div>
    </body>
</html>