In this sample HeatMapAPI layer is a added as custom dynamic map service layer to the ArcGIS JavaScript API and overlayed on top of a ArcGIS Online base map.

The points for the heat map is generated by querying the Population field from the states layer in the ESRI_Census_USA map service hosted on sampleserver1 (link). Once the query results are returned, the HeatMapAPI url is generated and shown on the map. Changing the extent of the map regenerates the image.

This sample uses free version of HeatMapAPI which is limited to 100 points.