Use a fallback image | TrackAsia GL JS Docs

Use a coalesce expression to display another image when a requested image is not available.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Use a fallback image</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>
<div id="map"></div>
<script>
var map = new trackasiagl.Map({
container: 'map',
style: 'https://maps.track-asia.com/styles/v1/streets.json?key=public_key',
center: [108.223071,16.109343],
zoom: 12
});
map.on('load', function () {
map.addSource('points', {
'type': 'geojson',
'data': {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [108.226592,16.106869]
},
'properties': {
'title': 'Danang City',
'icon': 'not-exists'
}
},
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [108.220923,16.095242]
},
'properties': {
'title': 'Thuan Phuoc Bridge',
'icon': 'bridge'
}
},
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [108.216494,16.119815]
},
'properties': {
'title': 'Tien Sa Port',
'icon': 'harbor'
}
}
]
}
});
map.addLayer({
'id': 'points',
'type': 'symbol',
'source': 'points',
'layout': {
'icon-image': [
'coalesce',
['image', ['concat', ['get', 'icon'], '']],
['image', 'marker']
],
'text-field': ['get', 'title'],
'text-font': ['Open Sans Semibold'],
'text-offset': [0, 0.6],
'text-anchor': 'top'
}
});
});
</script>
 
</body>
</html>