ArcGIS JS API - Masking a Layer - Changing the tilelayer source?

Question

I am trying to reproduce and modify the mask effect found in this example from the ArcGIS JS API:

Masking effect using a custom layer view

There is a lot of fancy footwork to modify the underlying tile layer and apply the mask effect based on a polygon feature layer. One thing I cannot seem to understand is how the underlying tile set is being called, and how I can change it. It seems that this example is using the esri terrain / world imagery tile set, but I don't see where that is being referenced. I want to try to recreate this mask effect using a different layer underneath, but I can't seem to find where I might reference a different layer to use underneath the mask. What am I missing?

Answer 1

I think you are talking about the basemap. The example uses ESRI World Imagery service, and it is set on map creation,

const map = new Map({
  basemap: "satellite", // <- here
  layers: [layer]
});

ArcGIS API - Map basemap