MapboxGL styles toggle

<!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/v0.5.2/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.5.2/mapbox-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>
mapboxgl.accessToken = 'pk.eyJ1IjoiZmFyYWRheTIiLCJhIjoiTUVHbDl5OCJ9.buFaqIdaIM3iXr1BOYKpsQ';
mapboxgl.util.getJSON('https://www.mapbox.com/mapbox-gl-styles/styles/outdoors-v6.json', function (err, style) {
  if (err) throw err;

// Set the global transition property in the stylesheet
  style.transition = {
    duration: 1000, // 1 second
    delay: 0
  };

var map = new mapboxgl.Map({
    container: 'map',
    style: style,
    center: [33.973142, 23.796679],
    zoom: 3
  });

window.setInterval(function() {
    if (map.style.classes.night) {
      map.style.removeClass('night');
    } else {
      map.style.addClass('night');
    }
  }, 20000);
});
</script>

</body>
</html>

https://api.tiles.mapbox.com/mapbox-gl-js/v0.5.2/mapbox-gl.js