# `Data Binding in Angular`

Data-binding in Angular web apps is the automatic synchronization of data between the model and view components. The way that Angular implements data-binding lets you treat the model as the single-source-of-truth in your application. The view is a projection of the model at all times. When the model changes, the view reflects the change, and vice versa.

## Data Binding in Classical Template Systems

Most templating systems bind data in only one direction: they merge template and model components together into a view, as illustrated in the diagram. After the merge occurs, changes to the model or related sections of the view are NOT automatically reflected in the view. Worse, any changes that the user makes to the view are not reflected in the model. This means that the developer has to write code that constantly syncs the view with the model and the model with the view.

## Data Binding in Angular Templates

The way Angular templates works is different, as illustrated in the diagram. They are different because first the template (which is the uncompiled HTML along with any additional markup or directives) is compiled on the browser, and second, the compilation step produces a live view. We say live because any changes to the view are immediately reflected in the model, and any changes in the model are propagated to the view. This makes the model always the single-source-of-truth for the application state, greatly simplifying the programming model for the developer. You can think of the view as simply an instant projection of your model.

Because the view is just a projection of the model, the controller is completely separated from the view and unaware of it. This makes testing a snap because it is easy to test your controller in isolation without the view and the related DOM/browser dependency.

## Related Topics

- Angular Scopes
- Angular Templates