Angular bidirectional data binding

Angular Templates Data bidirectional binding

The template (so-called template is HTML with markup and directives not compiled) is compiled in the browser,
The compilation process produces a dynamic view, and any changes to the view are mapped directly to the model, and any changes on the model are synchronized to the view. Model is a one-way source application state, greatly simplifying the developer's programming model. You can think of view as a simple map instance of model.
Because view is just a map of the model, the controller is completely separate from the view. This makes the test controller extremely simple because the test controller can be done independently, without relying on dom/browser.

Excerpt from: https://docs.angularjs.org/guide/databinding