Even though the function is called the same, Nathan is showing the Client API documentation here. The question is I think about the Pluggable widget API. In the Pluggable Widget API you can do something like props.attributeName.get(ObjectItem).value
The object item is the Mendix object retrieved from the datasource via the Pluggable Widget API. The props.attributeName is an attribute which should be configured as an attribute of the datasource object in the widget XML.
There are many new widgets using this type of code. See for instance my Google Maps widgets, Google Maps Polygon (React) or Google Maps Custom Marker (React) both available in the Marketplace and code on GitHub