Informative properties on Web Components

I would like to provide a set of read-only informative properties on a Dojo web component that can be used to interrogate the state of the widget. For example, properties on HTMLMediaElement like `duration`, `ended`, and `error` provide information without allowing the consumer of the element a way to directly change these values.

This problem may be two-fold.

* How do I update a property from inside a Dojo widget when using web components?
* How do I make a web component property read-only?

How can we solve this problem so a Dojo web component can provide informative read-only properties?