javascript - How to add a polygon from PostGIS ST_AsGeoJSON into Leaflet?

I try to use the following function to add polygons to my Leaflet map.

function polygon(geojson)
{

    alert(geojson); // alert for testing
    layer = L.geoJson(geojson);
    layer.addTo(map);
}

When I call the above function with the GeoJSON string I fetched from a PostGIS table using ST_AsGeoJSON(), the following string is alterted.

{"type":"Polygon","coordinates":[[[10,370],[20,380],[30,410],[-10,395],[10,370]]]}

But no polygon shows up on the map. As far as I can say, there is no error message. And I can definitely say that a polygon with the points 10 370, 20 380, 30 410, 10 395 shows up on the map, if I insert it using L.polygon.

What's wrong?

Answer

According to the docs, ST_AsGeoJSON() returns the geometry as a GeoJSON element. It does not return a whole GeoJSON object. Here is an example of a full GeoJSON object:

{
    "type": "Feature",
    "id": "OpenLayers.Feature.Vector_314",
    "properties": {},
    "geometry": {
        "type": "Point",
        "coordinates": [
            97.03125,

            39.7265625
        ]
    },
    "crs": {
        "type": "name",
        "properties": {
            "name": "urn:ogc:def:crs:OGC:1.3:CRS84"
        }
    }
}

The .geoJson method expects GeoJSON whereas ST_AsGeoJSON() only returns the geometry element and not the whole GeoJSON, that's why the method fails and nothing is plotted.