What to Do When ngOnInit Is Not Executing

Let me share my troubleshooting approach when dealing with ngOnInit issues, based on real scenarios I’ve encountered in enterprise applications.

Common causes I’ve encountered:

1. Component not properly declared/imported
2. Lifecycle hooks not implemented correctly
3. Route configuration issues
4. Dependency injection problems
5. Component initialization errors

Here’s my systematic approach:

// 1. Proper Component Setup
@Component({
  selector: 'app-problematic',
  template: `<div>{{ data() }}</div>`,
  standalone: true
})
export class ProblematicComponent implements OnInit {
  private logger = inject(LoggingService);
  
  data = signal<any>(null);
  
  // Add debugging logs
  constructor() {
    this.logger.debug('Constructor called');
  }
  
  ngOnInit() {
    this.logger.debug('ngOnInit called');
    this.loadData();
  }
  
  private loadData() {
    try {
      // Implementation
    } catch (error) {
      this.logger.error('Failed to load data', error);
    }
  }
}

// 2. Route Configuration Check
const routes: Routes = [
  {
    path: 'feature',
    loadChildren: () => import('./feature/feature.routes')
  }
];

// feature.routes.ts
export const FEATURE_ROUTES: Routes = [
  {
    path: '',
    component: FeatureComponent,
    resolve: {
      data: FeatureResolver
    }
  }
];

// 3. Resolver Implementation
@Injectable({ providedIn: 'root' })
export class FeatureResolver implements Resolve<any> {
  resolve(
    route: ActivatedRouteSnapshot,
    state: RouterStateSnapshot
  ): Observable<any> {
    return this.dataService.getData().pipe(
      catchError(error => {
        console.error('Resolver failed', error);
        return of(null);
      })
    );
  }
}

// 4. Component with Proper Error Handling
@Component({
  selector: 'app-feature',
  template: `
    @if (error()) {
      <error-alert [message]="error()" />
    }
    
    @if (data(); as componentData) {
      <div>{{ componentData.title }}</div>
    }
  `
})
export class FeatureComponent implements OnInit {
  private route = inject(ActivatedRoute);
  private logger = inject(LoggingService);
  private destroy$ = inject(DestroyRef);
  
  data = signal<any>(null);
  error = signal<string | null>(null);
  
  constructor() {
    this.logger.debug(
      'FeatureComponent constructor',
      { timestamp: new Date() }
    );
  }
  
  ngOnInit() {
    this.logger.debug(
      'FeatureComponent ngOnInit',
      { timestamp: new Date() }
    );
    
    // Get resolved data
    this.route.data.pipe(
      takeUntilDestroyed(this.destroy$)
    ).subscribe({
      next: (data) => {
        this.data.set(data);
        this.logger.debug('Data loaded', data);
      },
      error: (err) => {
        this.error.set('Failed to load data');
        this.logger.error('Data loading failed', err);
      }
    });
  }
}

// 5. Debugging Service
@Injectable({ providedIn: 'root' })
export class DebuggingService {
  private logger = inject(LoggingService);
  
  trackComponentLifecycle(
    component: any,
    componentName: string
  ) {
    return {
      onConstruct: () => {
        this.logger.debug(`${componentName} constructed`, {
          timestamp: new Date(),
          component
        });
      },
      
      onInit: () => {
        this.logger.debug(`${componentName} initialized`, {
          timestamp: new Date(),
          component
        });
      },
      
      onDestroy: () => {
        this.logger.debug(`${componentName} destroyed`, {
          timestamp: new Date(),
          component
        });
      }
    };
  }
}

Key points I emphasize in interviews:

1. Systematic Debugging

   • Check component declaration
   • Verify module imports
   • Review route configuration
   • Check dependency injection

2. Common Issues

   • Incorrect module setup
   • Missing implementations
   • Route configuration errors
   • Dependency injection problems

3. Best Practices

   • Implement proper error handling
   • Add debugging logs
   • Use lifecycle hooks correctly
   • Follow Angular best practices

4. Prevention

   • Use TypeScript strictly
   • Implement proper testing
   • Follow component lifecycle
   • Add error boundaries

This approach has helped me quickly identify and resolve ngOnInit issues in large Angular applications.