有人用过arcgis api for javascript吗，求教

Question

 function teatbuffer() {
                    var gsvc = new esri.tasks.GeometryService("http://tasks.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer");                    esriConfig.defaults.io.proxyUrl = "/proxy";
                    esriConfig.defaults.io.alwaysUseProxy = false;
                
                    var params = new esri.tasks.BufferParameters();
                    params.distances = "25";
                    params.bufferSpatialReference = new esri.SpatialReference({ wkid: 4326 });
                    params.outSpatialReference = map.spatialReference;
                    params.unit = "UNIT_METER";                    var geo = new esri.geometry.Point(120, 36);
                    var graphic = new esri.Graphic(geo, new esri.symbol.SimpleMarkerSymbol(esri.symbol.SimpleMarkerSymbol.STYLE_CIRCLE, 10,
                                        new esri.symbol.SimpleLineSymbol(esri.symbol.SimpleLineSymbol.STYLE_SOLID,
                                        new dojo.Color([100, 0, 0]), 1),
                                        new dojo.Color([255, 255, 0, 1])));
                    params.geometries = geo;
                    map.graphics.add(graphic);
                    gsvc.buffer(params, showBuffer);
                    
                    
                }
                
                
                
                //显示缓冲区
                function showBuffer(bufferedGeometries) {
                    var symbol = new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID,new SimpleLineSymbol(SimpleLineSymbol.STYLE_SOLID,new Color([255, 0, 0, 0.65]), 2),new Color([255, 0, 0, 0.35]));                    array.forEach(bufferedGeometries, function(geometry) {
                        var graphic = new Graphic(geometry, symbol);
                        map.graphics.add(graphic);
                    });
                }
画一个点的缓冲区，执行到 gsvc.buffer(params, showBuffer);就报错 dt.join is not a function
求教大神解决