The map reference lists the available basemaps which can be specified using the keyword:

Valid values are: "streets" , "satellite" , "hybrid", "topo", "gray", "oceans",
"national-geographic", "osm". 

You can add other layers as a basemap by finding their REST endpoint and adding them as a tiled layer. There's a example script here.

The map reference lists the available basemaps which can be specified using the keyword:

Valid values are: "streets" , "satellite" , "hybrid", "topo", "gray", "oceans",
"national-geographic", "osm". 

You can add other layers as a basemap by finding their REST endpoint and adding them as a tiled layer. There's a example script here.

The Esri Terrain layer seems to be coming from http://services.arcgisonline.com/arcgis/rest/services/World_Terrain_Base/MapServer

The labels seem to be coming from http://services.arcgisonline.com/ArcGIS/rest/services/Reference/World_Reference_Overlay/MapServer

You can add these two layers manually to reproduce the Terrain With Labels basemap combination.