Add some basic markers to a map in mapbox via mapb

I have a map styled with mapbox studio, however I'm having difficulty adding even a basic marker to it, however text is appearing where the marker should be which suggests that the marker would be there.

So here's the code with that map style:

mapboxgl.accessToken = 'pk.eyJ1Ijoic21pY2tpZSIsImEiOiJjaWtiM2JkdW0wMDJudnRseTY0NWdrbjFnIn0.WxGYL18BJjWUiNIu-r3MSA';
var map = new mapboxgl.Map({
    container: 'map',
    style: "mapbox://styles/smickie/cikb3fhvi0063cekqns0pk1f1",
    center: [-30.50, 40],
    zoom: 2,
    interactive: false
});

And here some markers being added from an example in the api:

map.on('style.load', function () {

    map.addSource("markers", {
        "type": "geojson",
        "data": {
            "type": "FeatureCollection",
            "features": [{
                "type": "Feature",
                "geometry": {
                    "type": "Point",
                    "coordinates": [-77.03238901390978, 38.913188059745586]
                },
                "properties": {
                    "title": "Mapbox DC",
                    "marker-symbol": "monument"
                }
            }, {
                "type": "Feature",
                "geometry": {
                    "type": "Point",
                    "coordinates": [-122.414, 37.776]
                },
                "properties": {
                    "title": "Mapbox SF",
                    "marker-color": "#ff00ff"
                }
            }]
        }
    });

    map.addLayer({
        "id": "markers",
        "type": "symbol",
        "source": "markers",
        "layout": {
            "icon-image": "{marker-symbol}-15",
            "text-field": "{title}",
            "text-font": ["Open Sans Semibold", "Arial Unicode MS Bold"],
            "text-offset": [0, 0.6],
            "text-anchor": "top"
        }
    });
});

However only the text and not the icons appear.

Question is: how would I add just a normal basic colored marker to this map, not even one of the special icon ones?

Thanks.

Problem here is that the starting point of your style in Mapbox Studio, the template you chose, doesn't have the glyphs/sprites you're referencing in your layer layout. If you switch to the same style they're using in the example you've used: mapbox://styles/mapbox/streets-v8 you'll see that the markers will appear. It's because they've been added to that style. If you switch back to your style, they're gone again.

Here's a console.log of your style's sprites:

And here's a console.log of Mapbox streets sprites:

As you can see, you have only two while mapbox has dozens (more than on the screenshot). You can use the ones you have by simply using the propertynames: default_marker and secondary_marker:

{
    "type": "Feature",
    "geometry": {
        "type": "Point",
        "coordinates": [-77.03238901390978, 38.913188059745586]
    },
    "properties": {
       "title": "Mapbox DC",
       "marker-symbol": "default_marker"
    }
}

map.addLayer({
    "id": "markers",
    "source": "markers",
    "type": "symbol",
    "layout": {
        "icon-image": "{marker-symbol}",
        "text-field": "{title}",
        "text-font": ["Open Sans Semibold", "Arial Unicode MS Bold"],
        "text-offset": [0, 0.6],
        "text-anchor": "top"
    }
});

Example on Plunker: http://plnkr.co/edit/W7pfGHVBzJj8U3AmPyzf?p=preview

If you need more you've got to add the sprites/glyphs you want to use to your style in Mapbox studio. Unfortunately this has little to do with "programming" since it's related to Mapbox Studio which is a software tool and thus kind of "offtopic" here on stackoverflow.

If you don't even need sprite/glyphs you could also use type: circle and the paint properties to create simple circles:

map.addLayer({
    "id": "markers",
    "source": "markers",
    "type": "circle",
    "paint": {
        "circle-radius": 10,
        "circle-color": "#007cbf"
    }
});

Example on Plunker: http://plnkr.co/edit/QDtIBtDIimKy6TUmKxcC?p=preview

More on styles and sprites can be found here: