Angular Component

Angular Component Development Workflow

Pre-Flight Checklist

• Identify correct app: playground-text-snippet, employee, etc.
• Read the design system docs for the target application (see below)
• Search for similar components: grep "{FeatureName}Component" --include="*.ts"
• Determine component type (list, form, detail, dialog)
• Check if store is needed (complex state)

🎨 Design System Documentation (MANDATORY)

Before creating any component, read the design system documentation for your target application:

Key docs to read:

• README.md - Component overview, base classes, library summary
• 02-component-catalog.md - Available components and usage examples
• 01-design-tokens.md - Colors, typography, spacing tokens
• 07-technical-guide.md - Implementation checklist

Component Hierarchy

PlatformComponent                    # Base: lifecycle, subscriptions, signals
├── PlatformVmComponent             # + ViewModel injection
├── PlatformFormComponent           # + Reactive forms integration
└── PlatformVmStoreComponent        # + ComponentStore state management

AppBaseComponent                     # + Auth, roles, company context
├── AppBaseVmComponent              # + ViewModel + auth context
├── AppBaseFormComponent            # + Forms + auth + validation
└── AppBaseVmStoreComponent         # + Store + auth + loading/error

Component Type Decision

File Location

src/PlatformExampleAppWeb/apps/{app-name}/src/app/
└── features/
    └── {feature}/
        ├── {feature}.component.ts
        ├── {feature}.component.html
        ├── {feature}.component.scss
        └── {feature}.store.ts (if using store)

Component HTML Template Standard (BEM Classes)

All UI elements in component templates MUST have BEM classes, even without styling needs. This makes HTML self-documenting like OOP class hierarchy.

<!-- ✅ CORRECT: All elements have BEM classes for structure clarity -->
<div class="feature-list">
    <div class="feature-list__header">
        <h1 class="feature-list__title">Features</h1>
        <button class="feature-list__btn --add" (click)="onAdd()">Add New</button>
    </div>
    <div class="feature-list__content">
        @for (item of vm.items; track trackByItem) {
        <div class="feature-list__item">
            <span class="feature-list__item-name">{{ item.name }}</span>
            <div class="feature-list__item-actions">
                <button class="feature-list__item-btn" (click)="onDelete(item)">Delete</button>
            </div>
        </div>
        } @empty {
        <div class="feature-list__empty">No items found</div>
        }
    </div>
</div>

<!-- ❌ WRONG: Elements without classes - structure unclear -->
<div class="feature-list">
    <div>
        <h1>Features</h1>
        <button (click)="onAdd()">Add New</button>
    </div>
    <div>
        @for (item of vm.items; track trackByItem) {
        <div>
            <span>{{ item.name }}</span>
            <div>
                <button (click)="onDelete(item)">Delete</button>
            </div>
        </div>
        }
    </div>
</div>

BEM Naming Convention:

• Block: Component name (e.g., feature-list)
• Element: Child using block__element (e.g., feature-list__header)
• Modifier: Separate class with -- prefix (e.g., feature-list__btn --add --large)

Component SCSS Standard

Always style both the host element (Angular selector) and the main wrapper class:

@import '~assets/scss/variables';

// Host element styling - ensures Angular element is a proper block container
my-component {
    display: flex;
    flex-direction: column;
}

// Main wrapper class with full styling
.my-component {
    display: flex;
    flex-direction: column;
    width: 100%;
    flex-grow: 1;

    &__header {
        // BEM child elements...
    }

    &__content {
        flex: 1;
        overflow-y: auto;
    }
}

Why both?

• Host element: Makes the Angular element a real layout element (not an unknown element without display)
• Main class: Contains the full styling, matches the wrapper div in HTML

Pattern 1: List Component with Store

Store Definition

// {feature}.store.ts
import { Injectable } from '@angular/core';
import { PlatformVmStore } from '@libs/platform-core';

export interface FeatureListState {
    items: FeatureDto[];
    selectedItem?: FeatureDto;
    filters: FeatureFilters;
}

@Injectable()
export class FeatureListStore extends PlatformVmStore<FeatureListState> {
    // Initial state
    protected override vmConstructor = (data?: Partial<FeatureListState>) => ({ items: [], filters: {}, ...data }) as FeatureListState;

    // Selectors
    public readonly items$ = this.select(state => state.items);
    public readonly selectedItem$ = this.select(state => state.selectedItem);

    // Effects
    public loadItems = this.effectSimple(() =>
        this.featureApi.getList(this.currentVm().filters).pipe(
            this.observerLoadingErrorState('loadItems'),
            this.tapResponse(items => this.updateState({ items }))
        )
    );

    public saveItem = this.effectSimple((item: FeatureDto) =>
        this.featureApi.save(item).pipe(
            this.observerLoadingErrorState('saveItem'),
            this.tapResponse(saved => {
                this.updateState(state => ({
                    items: state.items.upsertBy(x => x.id, [saved])
                }));
            })
        )
    );

    public deleteItem = this.effectSimple((id: string) =>
        this.featureApi.delete(id).pipe(
            this.observerLoadingErrorState('deleteItem'),
            this.tapResponse(() => {
                this.updateState(state => ({
                    items: state.items.filter(x => x.id !== id)
                }));
            })
        )
    );

    constructor(private featureApi: FeatureApiService) {
        super();
    }
}

List Component

// {feature}-list.component.ts
import { Component, OnInit } from '@angular/core';
import { AppBaseVmStoreComponent } from '@libs/apps-domains';
import { FeatureListStore, FeatureListState } from './feature-list.store';

@Component({
    selector: 'app-feature-list',
    templateUrl: './feature-list.component.html',
    styleUrls: ['./feature-list.component.scss'],
    providers: [FeatureListStore] // Provide store at component level
})
export class FeatureListComponent extends AppBaseVmStoreComponent<FeatureListState, FeatureListStore> implements OnInit {
    // Track-by for performance
    trackByItem = this.ngForTrackByItemProp<FeatureDto>('id');

    constructor(store: FeatureListStore) {
        super(store);
    }

    ngOnInit(): void {
        this.store.loadItems();
    }

    onRefresh(): void {
        this.reload(); // Reloads all store data
    }

    onDelete(item: FeatureDto): void {
        this.store.deleteItem(item.id);
    }

    // Check loading state for specific request
    get isDeleting$() {
        return this.store.isLoading$('deleteItem');
    }
}

List Template

<!-- {feature}-list.component.html -->
<app-loading-and-error-indicator [target]="this">
    @if (vm(); as vm) {
    <div class="feature-list">
        <!-- Header with actions -->
        <div class="header">
            <h1>Features</h1>
            <button (click)="onRefresh()" [disabled]="isStateLoading()()">Refresh</button>
        </div>

        <!-- List items -->
        @for (item of vm.items; track trackByItem) {
        <div class="item">
            <span>{{ item.name }}</span>
            <button (click)="onDelete(item)" [disabled]="isDeleting$() === true">Delete</button>
        </div>
        } @empty {
        <div class="empty">No items found</div>
        }
    </div>
    }
</app-loading-and-error-indicator>

Pattern 2: Form Component

// {feature}-form.component.ts
import { Component } from '@angular/core';
import { FormControl, Validators } from '@angular/forms';
import { AppBaseFormComponent } from '@libs/apps-domains';
import { ifAsyncValidator, noWhitespaceValidator } from '@libs/platform-core';

export interface FeatureFormVm {
    id?: string;
    name: string;
    code: string;
    status: FeatureStatus;
    effectiveDate?: Date;
}

@Component({
    selector: 'app-feature-form',
    templateUrl: './feature-form.component.html'
})
export class FeatureFormComponent extends AppBaseFormComponent<FeatureFormVm> {
    // Form configuration
    protected initialFormConfig = () => ({
        controls: {
            name: new FormControl(this.currentVm().name, [Validators.required, Validators.maxLength(200), noWhitespaceValidator]),
            code: new FormControl(
                this.currentVm().code,
                [Validators.required, Validators.pattern(/^[A-Z0-9-]+$/)],
                [
                    // Async validator only runs if sync validators pass
                    ifAsyncValidator(() => !this.isViewMode(), this.checkCodeUniqueValidator())
                ]
            ),
            status: new FormControl(this.currentVm().status, [Validators.required]),
            effectiveDate: new FormControl(this.currentVm().effectiveDate)
        },
        // Re-validate code when status changes
        dependentValidations: {
            code: ['status']
        }
    });

    // Initialize or reload view model
    protected initOrReloadVm = (isReload: boolean) => {
        if (this.mode === 'create') {
            return of<FeatureFormVm>({
                name: '',
                code: '',
                status: FeatureStatus.Draft
            });
        }
        return this.featureApi.getById(this.featureId);
    };

    // Custom async validator
    private checkCodeUniqueValidator() {
        return async (control: AbstractControl) => {
            const exists = await firstValueFrom(this.featureApi.checkCodeExists(control.value, this.currentVm().id));
            return exists ? { codeExists: true } : null;
        };
    }

    onSubmit(): void {
        if (!this.validateForm()) return;

        const vm = this.currentVm();
        this.featureApi
            .save(vm)
            .pipe(
                this.observerLoadingErrorState('save'),
                this.tapResponse(
                    saved => this.onSaveSuccess(saved),
                    error => this.onSaveError(error)
                ),
                this.untilDestroyed()
            )
            .subscribe();
    }

    constructor(private featureApi: FeatureApiService) {
        super();
    }
}

Form Template

<!-- {feature}-form.component.html -->
<form [formGroup]="form" (ngSubmit)="onSubmit()">
    <!-- Name field -->
    <div class="form-field">
        <label for="name">Name *</label>
        <input id="name" formControlName="name" />
        @if (formControls('name').errors?.['required']) {
        <span class="error">Name is required</span>
        }
    </div>

    <!-- Code field with async validation -->
    <div class="form-field">
        <label for="code">Code *</label>
        <input id="code" formControlName="code" />
        @if (formControls('code').errors?.['codeExists']) {
        <span class="error">Code already exists</span>
        } @if (formControls('code').pending) {
        <span class="info">Checking...</span>
        }
    </div>

    <!-- Status dropdown -->
    <div class="form-field">
        <label for="status">Status *</label>
        <select id="status" formControlName="status">
            @for (status of statusOptions; track status.value) {
            <option [value]="status.value">{{ status.label }}</option>
            }
        </select>
    </div>

    <!-- Actions -->
    <div class="actions">
        <button type="button" (click)="onCancel()">Cancel</button>
        <button type="submit" [disabled]="!form.valid || isLoading$('save')()">{{ isLoading$('save')() ? 'Saving...' : 'Save' }}</button>
    </div>
</form>

Pattern 3: Simple Component

// {feature}-card.component.ts
import { Component, Input, Output, EventEmitter } from '@angular/core';
import { AppBaseComponent } from '@libs/apps-domains';

@Component({
    selector: 'app-feature-card',
    template: `
        <div class="card" [class.selected]="isSelected">
            <h3>{{ feature.name }}</h3>
            <p>{{ feature.description }}</p>
            @if (canEdit) {
                <button (click)="onEdit.emit(feature)">Edit</button>
            }
        </div>
    `
})
export class FeatureCardComponent extends AppBaseComponent {
    @Input() feature!: FeatureDto;
    @Input() isSelected = false;
    @Output() EventEmitter<FeatureDto>();

    get canEdit(): boolean {
        return this.hasRole('Admin', 'Manager');
    }
}

Key Platform APIs

Lifecycle & Subscriptions

// Auto-cleanup subscription
this.data$.pipe(this.untilDestroyed()).subscribe();

// Store named subscriptions
this.storeSubscription('key', observable.subscribe());
this.cancelStoredSubscription('key');

Loading/Error State

// Track request state
observable.pipe(this.observerLoadingErrorState('requestKey'));

// Check states in template
isLoading$('requestKey')();
getErrorMsg$('requestKey')();
isStateLoading()();
isStateError()();

Response Handling

// Handle success/error
observable.pipe(
    this.tapResponse(
        result => {
            /* success */
        },
        error => {
            /* error */
        }
    )
);

Track-by Functions

// For @for loops
trackByItem = this.ngForTrackByItemProp<Item>('id');
trackByList = this.ngForTrackByImmutableList(this.items);

Code Responsibility Hierarchy (CRITICAL)

Place logic in the LOWEST appropriate layer to enable reuse and prevent duplication:

// ❌ WRONG: Logic in component (leads to duplication if another component needs it)
readonly authTypes = [{ value: AuthType.OAuth2, label: 'OAuth2' }, ...];
getDefaultBaseUrl(type) { return this.providerUrls[type] ?? ''; }

// ✅ CORRECT: Logic in entity/model (single source of truth, reusable)
readonly authTypes = AuthConfigurationDisplay.getApiAuthTypeOptions();
getDefaultBaseUrl(type) { return JobBoardProviderConfiguration.getDefaultBaseUrl(type); }

Common Refactoring Patterns:

• Dropdown options → static method in entity: Entity.getOptions()
• Display logic (CSS class, text) → instance method in entity: entity.getStatusCssClass()
• Default values → static method in entity: Entity.getDefaultValue()
• Command building → factory class in service: CommandFactory.buildSaveCommand(formValues)

Anti-Patterns to AVOID

:x: Using wrong base class

// WRONG - using PlatformComponent when auth needed
export class MyComponent extends PlatformComponent {}

// CORRECT - using AppBaseComponent for auth context
export class MyComponent extends AppBaseComponent {}

:x: Manual subscription management

// WRONG
private sub: Subscription;
ngOnDestroy() { this.sub.unsubscribe(); }

// CORRECT
this.data$.pipe(this.untilDestroyed()).subscribe();

:x: Direct HTTP calls

// WRONG
constructor(private http: HttpClient) { }

// CORRECT
constructor(private featureApi: FeatureApiService) { }

:x: Missing loading states

<!-- WRONG - no loading indicator -->
<div>{{ items }}</div>

<!-- CORRECT - with loading wrapper -->
<app-loading-and-error-indicator [target]="this">
    <div>{{ items }}</div>
</app-loading-and-error-indicator>

Verification Checklist

• Correct base class selected for use case
• Store provided at component level (if using store)
• Loading/error states handled with app-loading-and-error-indicator
• Subscriptions use untilDestroyed()
• Track-by functions used in @for loops
• Form validation configured properly
• Auth checks use hasRole() from base class
• API calls use service extending PlatformApiService