Angular Architect

Key Patterns

Standalone Component with OnPush and Signals

import { ChangeDetectionStrategy, Component, computed, input, output, signal } from '@angular/core';
import { CommonModule } from '@angular/common';

@Component({
  selector: 'app-user-card',
  standalone: true,
  imports: [CommonModule],
  changeDetection: ChangeDetectionStrategy.OnPush,
  template: `
    <div class="user-card">
      <h2>{{ fullName() }}</h2>
      <button (click)="onSelect()">Select</button>
    </div>
  `,
})
export class UserCardComponent {
  firstName = input.required<string>();
  lastName = input.required<string>();
  selected = output<string>();

  fullName = computed(() => `${this.firstName()} ${this.lastName()}`);

  onSelect(): void {
    this.selected.emit(this.fullName());
  }
}

RxJS Subscription Management with takeUntilDestroyed

import { Component, OnInit, inject } from '@angular/core';
import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
import { UserService } from './user.service';

@Component({ selector: 'app-users', standalone: true, template: `...` })
export class UsersComponent implements OnInit {
  private userService = inject(UserService);
  // DestroyRef is captured at construction time for use in ngOnInit
  private destroyRef = inject(DestroyRef);

  ngOnInit(): void {
    this.userService.getUsers()
      .pipe(takeUntilDestroyed(this.destroyRef))
      .subscribe({
        next: (users) => { /* handle */ },
        error: (err) => console.error('Failed to load users', err),
      });
  }
}

NgRx Action / Reducer / Selector

// actions
export const loadUsers = createAction('[Users] Load Users');
export const loadUsersSuccess = createAction('[Users] Load Users Success', props<{ users: User[] }>());
export const loadUsersFailure = createAction('[Users] Load Users Failure', props<{ error: string }>());

// reducer
export interface UsersState { users: User[]; loading: boolean; error: string | null; }
const initialState: UsersState = { users: [], loading: false, error: null };

export const usersReducer = createReducer(
  initialState,
  on(loadUsers, (state) => ({ ...state, loading: true, error: null })),
  on(loadUsersSuccess, (state, { users }) => ({ ...state, users, loading: false })),
  on(loadUsersFailure, (state, { error }) => ({ ...state, error, loading: false })),
);

// selectors
export const selectUsersState = createFeatureSelector<UsersState>('users');
export const selectAllUsers = createSelector(selectUsersState, (s) => s.users);
export const selectUsersLoading = createSelector(selectUsersState, (s) => s.loading);

Constraints

MUST DO

• Use standalone components (Angular 17+ default)
• Use signals for reactive state where appropriate
• Use OnPush change detection strategy
• Use strict TypeScript configuration
• Implement proper error handling in RxJS streams
• Use trackBy functions in *ngFor loops
• Write tests with >85% coverage
• Follow Angular style guide

MUST NOT DO

• Use NgModule-based components (except when required for compatibility)
• Forget to unsubscribe from observables (use takeUntilDestroyed or async pipe)
• Use async operations without proper error handling
• Skip accessibility attributes
• Expose sensitive data in client-side code
• Use any type without justification
• Mutate state directly in NgRx
• Skip unit tests for critical logic

Output Templates

When implementing Angular features, provide:

1. Component file with standalone configuration
2. Service file if business logic is involved
3. State management files if using NgRx
4. Test file with comprehensive test cases
5. Brief explanation of architectural decisions