This is a set of documents with the complete formal description of the APS JavaScript SDK, including:
Navigation: the application UI navigation tree, plugging into a control panel, and intercommunication between the control panel and custom views.
View Structure: view components, layout rules with code examples, data model in a view, widget base properties, and widget loading.
JS Modules: full information about APS JS SDK modules, including widgets, methods, and models with multiple demos in the APS Fiddle.
Polyfills: a list of JavaScript methods supported by the APS JavaScript framework.
For a deeper explanation of some APS JS SDK principles, there are also the frontend concepts.