How does Angular's injector hierarchy affect service lifetime?

Connects environment and element injectors to instance lifetime, overrides, lazy routes, and accidental state isolation.

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TL;DR

Angular resolves dependencies through hierarchical injectors. An application-level or root provider is shared broadly, a route provider can scope an instance to that route environment, and a component provider creates an instance for that component subtree. If the same token is provided closer to the requester, that nearer provider wins.

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Angular dependency injection, provider hierarchy, service lifetime, route scope, component scope, and debugging.

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Core answer first, then checkpoints toward a stronger answer.

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Core answer
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Overview
A provider declaration chooses both how a dependency is created and which part of the application shares it.
Angular resolves dependencies through hierarchical injectors. An application-level or root provider is shared broadly, a route provider can scope an instance to that route environment, and a component provider creates an instance for that component subtree. If the same token is provided closer to the requester, that nearer provider wins.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
I use root scope for stateless cross-application services, route scope for feature state that should reset when the route environment is destroyed, and component scope for genuinely local coordination. Providing a service again by accident can split caches or state into multiple instances, which often looks like updates disappearing. Angular checks the element injector path and then the environment injector hierarchy, so I inspect where the request originates and where each provider was registered. Scope is a behavior decision, not just configuration style.

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Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Assuming every injected service is an application singleton.
Providing a stateful service again in a child component unintentionally.
Using optional to hide a required dependency.

How does Angular's injector hierarchy affect service lifetime?

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