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docs: add change detection to glossary (#34316) 

PR Close #34316
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Judy Bogart 2019-12-09 10:56:57 -08:00 committed by Andrew Kushnir
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aio/content/guide/glossary.md
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@ -144,6 +144,23 @@ For example, "convert_link_mode".
* UPPER_UNDERSCORE_CASE (or UPPER_SNAKE_CASE, or SCREAMING_SNAKE_CASE): Traditional for constants (acceptable, but prefer camelCase). * UPPER_UNDERSCORE_CASE (or UPPER_SNAKE_CASE, or SCREAMING_SNAKE_CASE): Traditional for constants (acceptable, but prefer camelCase).
Upper snake case uses words in all capital letters connected with underscores. For example, "FIX_ME". Upper snake case uses words in all capital letters connected with underscores. For example, "FIX_ME".
{@a change-detection}
## change detection
The mechanism by which the Angular framework synchronizes the state of an application's UI with the state of the data.
The change detector checks the current state of the data model whenever it runs, and maintains it as the previous state to compare on the next iteration.
As the application logic updates component data, values that are bound to DOM properties in the view can change.
The change detector is responsible for updating the view to reflect the current data model.
Similarly, the user can interact with the UI, causing events that change the state of the data model.
These events can trigger change detection.
Using the default ("CheckAlways") change-detection strategy, the change detector goes through the [view hierarchy](#view-tree) on each VM turn to check every [data-bound property](#data-binding) in the template. In the first phase, it compares the current state of the dependent data with the previous state, and collects changes.
In the second phase, it updates the page DOM to reflect any new data values.
If you set the `OnPush` ("CheckOnce") change-detection strategy, the change detector runs only when [explicitly invoked] (api/core/ChangeDetectorRef), or when it is triggered by an `Input` reference change or event handler. This typically improves performance. For more information, see [Optimize Angular's change detection](https://web.dev/faster-angular-change-detection/).
{@a class-decorator} {@a class-decorator}
## class decorator ## class decorator
@ -938,7 +955,7 @@ View hierarchies can be loaded and unloaded dynamically as the user navigates th
## view hierarchy ## view hierarchy
A tree of related views that can be acted on as a unit. The root view is a component's *host view*. A host view can be the root of a tree of *embedded views*, collected in a *view container* (`ViewContainerRef`) attached to an anchor element in the hosting component. The view hierarchy is a key part of Angular change detection. A tree of related views that can be acted on as a unit. The root view is a component's *host view*. A host view can be the root of a tree of *embedded views*, collected in a *view container* (`ViewContainerRef`) attached to an anchor element in the hosting component. The view hierarchy is a key part of Angular [change detection](#change-detection).
The view hierarchy doesn't imply a component hierarchy. Views that are embedded in the context of a particular hierarchy can be host views of other components. Those components can be in the same NgModule as the hosting component, or belong to other NgModules. The view hierarchy doesn't imply a component hierarchy. Views that are embedded in the context of a particular hierarchy can be host views of other components. Those components can be in the same NgModule as the hosting component, or belong to other NgModules.