dependency-injection

name	Dependency Injection
description	Best practices for DI, inject() usage, and providers.
metadata	{"labels":["angular","di","injection","providers"],"triggers":{"files":["**/*.service.ts","**/*.ts"],"keywords":["angular inject","providedIn","injection token"]}}

Dependency Injection

Priority: P0 (CRITICAL)

Principles

• inject() over Constructor: Use the inject() function for cleaner injection updates and type inference.
• Tree Shaking: Always use providedIn: 'root' for services unless specific scoping is required.
• Tokens: Use InjectionToken<T> for configuration, primitives, or interface abstraction.

Guidelines

• Providers: Prefer provide* functions (e.g., provideHttpClient()) in app.config.ts over importing modules.
• Factories: Use useFactory strictly when dependencies need runtime configuration.

Anti-Patterns

• Global State: Avoid providedIn: 'platform' unless absolutely necessary (share between Micro Frontends).
• Circular Deps: Use forwardRef only as a last resort; refactor architecture instead.

References

• DI Patterns