displaying scale of dyamic map service layer using ArcGIS JS API

Question

In ArcGIS JS API, I would like to know and display the scale of a dynamic service layer by using the onExtentChange event, but the LOD argument is only valid for tile map services. Is there an equivalent way for dynamic map services?

Answer 1

The scale property applies to the map, not the individual layer, so you can use map.getScale() to display it.

You can get the map's level using map.getLevel(), but as you identified this only applies if there is a tiled layer in the map.

Answer 2

Instead of calculating scale on extentChange event , there is predefined scalebar in ArcGIS JS API, just add a scale bar widget while loading the map and give your map instance to ScaleBar widget like this ,

var scalebar = new Scalebar({
            map: this.currentMap,
            // "dual" displays both miles and kilometers
            // "english" is the default, which displays miles
            // use "metric" for kilometers
            scalebarUnit: "dual"
        });

https://developers.arcgis.com/javascript/3/jssamples/widget_scalebar.html