How to get LatLng array from geoJSON Layer in Leaflet?

i need to hand the latlng coordinates from my phpPostGIS-served geoJSONLayer as an array over to a new added HeatMap Layer. L.geoJSON has an build-in option: coordsToLatLng( coords )" and a static method for that: coordsToLatLngs( coords, levelsDeep?, reverse? ). I don´t get any errors, but the heat map does´t show up. If i build a new L.heatLayer(coord).addTo(map); outside the function, it works… Does anyone have an idea? This is what i have so far:

    $.getJSON("postgis_geojson.php?geotable=shops&geomfield=the_geom", function(data) {

        L.geoJson(data, {

            pointToLayer: function (feature, latlng) {
                return L.circleMarker(latlng, geojsonMarkerOptions);

            },
             onEachFeature: function (feature, layer) {
                 popupOptions = {maxWidth: 200};
                layer.bindPopup(feature.properties.popupContent);
            },
            coordsToLatLng: function (coords) {
            return new L.heatLayer(coords);

            }

        }).addTo(map);
        });

Answer

In OnEachFeature you can find the coordinates in feature.geometry.coordinates. so

   coords = []; //define an array to store coordinates
   onEachFeature: function (feature, layer) {
             popupOptions = {maxWidth: 200};
            layer.bindPopup(feature.properties.popupContent);

            coords.push(feature.geometry.coordinates);

}

Now you can use the array coords in L.heatLayer