Check for browser support
Check for Mapbox GL browser support
<!DOCTYPE html>
<html>
<head>
    <meta charset='utf-8' />
    <title></title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.37.0/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.37.0/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
</head>
<body>

<script src='https://api.mapbox.com/mapbox-gl-js/plugins/mapbox-gl-supported/v1.2.0/mapbox-gl-supported.js'></script>
<div id='map'></div>

<script>
mapboxgl.accessToken = '<your access token here>';
if (!mapboxgl.supported()) {
    alert('Your browser does not support Mapbox GL');
} else {
    var map = new mapboxgl.Map({
        container: 'map',
        style: 'mapbox://styles/mapbox/streets-v9',
        center: [-74.50, 40],
        zoom: 9
    });
}
</script>

</body>
</html>
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