Javascript – Mapbox GL JS getBounds()/fitBounds()

I'm using Mapbox GL JS v0.14.2 and I've searched high and low through the documentation and very little is clear about this.

If you use the standard JS API, it's very clear to 'fit map to markers' using an example they have provided (https://www.mapbox.com/mapbox.js/example/v1.0.0/fit-map-to-markers/); however the setup when using the GL api is quite different. The GL API has getBounds() (https://www.mapbox.com/mapbox-gl-js/api/#Map.getBounds) but because you don't have a named layer, like the standard JS API, so I'm struggling to work out how to use getBounds() at all.

I've found this (Mapbox GL JS API Set Bounds) but surely can't be the right answer?

This is the bulk of my setup; excluding JSON setup and other options.

mapboxgl.accessToken = '<myaccesstoken>';

var markers = <?php echo $programme_json; ?>;

var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/richgc/cikyo5bse00nqb0lxebkfn2bm',
    center: [-1.470085, 53.381129],
    zoom: 15
});

map.on('style.load', function() {
    map.addSource('markers', {
        'type': 'geojson',
        'data': markers
    });

    map.addLayer({
        "id": "markers",
        "interactive": true,
        "type": "symbol",
        "source": "markers",
        "layout": {
            "icon-image": "venue-map-icon-blue",
            'icon-size': 0.5,
            "icon-allow-overlap": true
        }
    });

    map.scrollZoom.disable();

});

I have tried the following:

alert(map.getBounds()); // LngLatBounds(LngLat(-1.4855345239256508, 53.37642500812015), LngLat(-1.4546354760740883, 53.38583247227842))
var bounds = [[-1.4855345239256508, 53.37642500812015],[-1.4546354760740883, 53.38583247227842]]
map.fitBounds(bounds);

So I know how to fitBounds, but I'm unsure how to get them map.getBounds() just seems to return the set centre position lng/lat.

Markers JSON:

var markers = {"type":"FeatureCollection","features":[{"type":"Feature","properties":{"title":"Site Gallery","url":"\/Freelance\/art-sheffield-2016\/programme\/site-gallery\/","summary":"Duis arcu tortor, suscipit eget, imperdiet nec, imperdiet iaculis, ipsum. Donec id justo. Aenean tellus metus, bibendum sed, posuere ac, mattis non, nunc. Suspendisse feugiat. Etiam rhoncus.","image":"\/Freelance\/art-sheffield-2016\/site\/assets\/files\/1032\/site_gallery.jpg","marker-symbol":"venue-map-icon-blue","colour":"blue"},"geometry":{"type":"Point","coordinates":["-1.466439","53.376842"]}},{"type":"Feature","properties":{"title":"Moore Street Substation","url":"\/Freelance\/art-sheffield-2016\/programme\/moore-street-substation\/","summary":"","image":null,"marker-symbol":"venue-map-icon-green","colour":"green"},"geometry":{"type":"Point","coordinates":["-1.477881","53.374798"]}},{"type":"Feature","properties":{"title":"S1 Artspace","url":"\/Freelance\/art-sheffield-2016\/programme\/s1-artspace\/","summary":"","image":null,"marker-symbol":"venue-map-icon-red","colour":"red"},"geometry":{"type":"Point","coordinates":["-1.459620","53.380562"]}}]};