JSON Output File Format - php

Question

I am using Canvasjs Charts to do my graphing from PHP / MySQL. Everything works as expected except for the creating of my JSON file.
Canvasjs requires the JSON file to look as follow:
callback({
"dps":
[{"division":"Xaxis VALUE","units":Yaxis VALUE}]
})
However, when creating my JSON file it is
[{"division":"Xaxis VALUE","units":Yaxis VALUE}]
All I want to know is how do I add the opening tag and closing tag in the sjon file from my script.
Here is the last part of my code that creates the JSON file:
$output_data= array();
while($row = mysqli_fetch_array($result))
{
$output_data[] = array(
'division' => $row["division"],
'units' => $row["units"]
);
}
return json_encode($output_data, JSON_NUMERIC_CHECK);
echo json_encode($output_data, JSON_NUMERIC_CHECK);
}
$file_name = 'myresult2'.'.json';
if(file_put_contents($file_name, get_data()))
{
echo $file_name. 'file created';
}
else
{
echo 'Error';
}
?>
Additional Data:
This is the code that generates the graph.
<script>
var chart = null;
var dataPoints = [];
window.onload = function() {
chart = new CanvasJS.Chart("chartContainer", {
animationEnabled: true,
theme: "light",
title: {
text: "Graph Header"
},
axisY: {
title: "% Verified",
titleFontSize: 12,
labelFontSize: 12,
valueFormatString: "#.##%"
},
axisX: {
title: "Division",
titleFontSize: 12,
labelFontSize: 12
},
data: [{
type: "column",
yValueFormatString: "#.##%",
dataPoints: dataPoints
}]
});
$.getJSON("myresult.json?callback=?", callback);
}
function callback(data) {
for (var i = 0; i < data.dps.length; i++) {
dataPoints.push({
label: data.dps[i].division,
y: data.dps[i].units
});
}
chart.render();
}
</script>

Answer 1

Please try
// change this
$output_data[] = array(
// to this
$output_data['dps'][] = array(

Answer 2

What you need to do is enclose you created array in a new array with a key named dps.
So after your while loop you should do something like this
$json_data['dps']=$output_data;
return json_encode($json_data, JSON_NUMERIC_CHECK);