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How does Angular's dependency resolution search work using @Self(), @SkipSelf(), @Optional(), and @Host()?

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01

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Explain resolution modifiers in Angular DI.

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03

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Resolution modifiers restrict or modify where the DI injector searches for dependencies: @Self() queries only the current component's injector; @SkipSelf() starts searching from the parent injector; @Host() stops searching at the template boundary; @Optional() prevents throwing an error if the token isn't found

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04

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Using resolution modifiers in a component constructor
import { Component, Optional, Self, SkipSelf, Host } from '@angular/core';

@Injectable()
export class LoggerService {}

@Component({
  selector: 'app-sandbox',
  providers: [LoggerService],
  template: '...'
})
export class SandboxComponent {
  constructor(
    @Self() private localLogger: LoggerService,
    @SkipSelf() private parentLogger: LoggerService,
    @Host() private hostLogger: LoggerService,
    @Optional() private optionalLogger: LoggerService | null
  ) {}
}
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