The controller concept

Controller is an object that exposes methods to dynamically control and interact with the IntlShape object, as well as getters to access the current controller state and additional locale data.

Controller is not a class

When you create a controller, you do not create a class; instead, multiple partials that are separated by their concerns are initialised and then stitched together to create the controller object.

None of the members of the controller object use this, so most of them can be safely extracted and used on their own if needed.

The choice to use object rather than class comes from maintainability concerns: a big class is much harder to navigate and decouple.

Other advantages include better support for minification: internal variables and functions can be easily mangled without breaking anything, while class properties usually retain their names.