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@workInProgress
@ngdoc overview
@name Developer Guide: Scopes: Updating Scope Properties
@description
You can update a scope by calling its {@link api/angular.scope.$eval $eval()} method, but usually
you do not have to do this explicitly. In most cases, angular intercepts all external events (such
as user interactions, XHRs, and timers) and calls the `$eval()` method on the scope object for you
at the right time. The only time you might need to call `$eval()` explicitly is when you create
your own custom widget or service.
The reason it is unnecessary to call `$eval()` from within your controller functions when you use
built-in angular widgets and services is because a change in the data model triggers a call to the
`$eval()` method on the scope object where the data model changed.
When a user inputs data, angularized widgets copy the data to the appropriate scope and then call
the `$eval()` method on the root scope to update the view. It works this way because scopes are
inherited, and a child scope `$eval()` overrides its parent's `$eval()` method. Updating the whole
page requires a call to `$eval()` on the root scope as `$root.$eval()`. Similarly, when a request
to fetch data from a server is made and the response comes back, the data is written into the model
and then `$eval()` is called to push updates through to the view and any other dependents.
A widget that creates scopes (such as {@link api/angular.widget.@ng:repeat ng:repeat}) is
responsible for forwarding `$eval()` calls from the parent to those child scopes. That way, calling
`$eval()` on the root scope will update the whole page. This creates a spreadsheet-like behavior
for your app; the bound views update immediately as the user enters data.
## Related Documents
* {@link dev_guide.scopes Angular Scope Objects}
* {@link dev_guide.scopes.understanding_scopes Understanding Angular Scope Objects}
* {@link dev_guide.scopes.working_scopes Working With Angular Scopes}
* {@link dev_guide.scopes.controlling_scopes Applying Controllers to Scopes}
## Related API
* {@link api/angular.scope Angular Scope API}
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