Show drawn polygon area | TrackAsia GL JS Docs

Use mapbox-gl-draw to draw a polygon and Turf.js to calculate its area in square meters.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Show drawn polygon area</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-gl.js"></script>
<link href="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-gl.css" rel="stylesheet" />
<style>
	body { margin: 0; padding: 0; }
	#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<style>
.calculation-box {
height: 75px;
width: 150px;
position: absolute;
bottom: 40px;
left: 10px;
background-color: rgba(255, 255, 255, 0.9);
padding: 15px;
text-align: center;
}
 
p {
font-family: 'Open Sans';
margin: 0;
font-size: 13px;
}
</style>
 
<script src="https://api.tiles.mapbox.com/mapbox.js/plugins/turf/v3.0.11/turf.min.js"></script>
<script src="https://api.mapbox.com/mapbox-gl-js/plugins/mapbox-gl-draw/v1.2.0/mapbox-gl-draw.js"></script>
<link
rel="stylesheet"
href="https://api.mapbox.com/mapbox-gl-js/plugins/mapbox-gl-draw/v1.2.0/mapbox-gl-draw.css"
type="text/css"
/>
<div id="map"></div>
<div class="calculation-box">
<p>Draw a polygon using the draw tools.</p>
<div id="calculated-area"></div>
</div>
 
<script>
var map = new trackasiagl.Map({
container: 'map', // container id
style: 'https://maps.track-asia.com/styles/v1/streets.json?key=public_key', //hosted style id
center: {"lat":10.762622,"lng":106.660172}, // starting position
zoom: 12 // starting zoom
});
 
var draw = new MapboxDraw({
displayControlsDefault: false,
controls: {
polygon: true,
trash: true
},
defaultMode: 'draw_polygon'
});
map.addControl(draw);
 
map.on('draw.create', updateArea);
map.on('draw.delete', updateArea);
map.on('draw.update', updateArea);
 
function updateArea(e) {
var data = draw.getAll();
var answer = document.getElementById('calculated-area');
if (data.features.length > 0) {
var area = turf.area(data);
// restrict to area to 2 decimal points
var rounded_area = Math.round(area * 100) / 100;
answer.innerHTML =
'<p><strong>' +
rounded_area +
'</strong></p><p>square meters</p>';
} else {
answer.innerHTML = '';
if (e.type !== 'draw.delete')
alert('Use the draw tools to draw a polygon!');
}
}
</script>
 
</body>
</html>