What is Zone.js and what does it do?
Model answer
Zone.js patches browser async APIs (events, timers, promises) so Angular is told when asynchronous work finishes. Angular then runs change detection. It makes updates feel automatic.
The downsides are extra bundle size, some overhead, and checks that may run when nothing changed. Angular is moving towards signals and zoneless operation, where updates are triggered by signals and explicit notifications rather than Zone.js.
Learn this topic
Angular Tutorial: Beginner to Advanced .
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