JavaScript编译时Uncaught TypeError: undefined is not a function

变量方法都是定义好的呀，下面是部分代码：
               function mapClickHandler(evt) {
                var stopP = new Point(evt.mapPoint.x, evt.mapPoint.y, myMap.spatialReference);          
                var stopPoint = new esri.Graphic(stopP);                
                stopsGraphicsLayer.add(stopPoint);  
                stops.features.push(stopPoint);         
                }
它这意思是哪个函数或变量未定义啊？