Change detection in Angular is the process of updating the view whenever the underlying component data changes. It's an important part of Angular's architecture, as it ensures that the view is always in sync with the component data.
Angular implements a unidirectional data flow, where the component data is updated first, and then the view is updated to reflect those changes. This is in contrast to traditional two-way data binding, where changes in the view can also trigger updates to the component data.
Angular uses a strategy called "dirty checking" for change detection. This involves checking the current values of all data-bound properties in the component and its children, and comparing them to their previous values. If any values have changed, the view is updated to reflect the changes.
By default, change detection is performed for the entire application tree whenever any user interaction takes place, such as a click event or a key press. This ensures that the view is always up-to-date with the latest component data.
However, for performance reasons, you can also control change detection manually using ChangeDetectorRef, where you can trigger a change detection cycle for a specific component or even turn it off completely.
In summary, change detection in Angular is a powerful mechanism that ensures that the view is always in sync with the component data, and it's a critical part of the Angular framework.