Obter polígono usando um extent como origem

obter_poligono_from_extent.js

obter_poligono: function(graphic, commontype)
{
    var geometry = graphic.geometry;
    var polygon = geometry;

    if(geometry.type === "extent")
    {
        var a = geometry;
        polygon = new Polygon(a.spatialReference);
        var r=[[a.xmin,a.ymin],
               [a.xmin,a.ymax],
               [a.xmax,a.ymax],
               [a.xmax,a.ymin],
               [a.xmin,a.ymin]];
        polygon.addRing(r);
        geometry = polygon;
        commontype = "polygon";
    }
    return polygon;
},