Angular UI Patterns

Core Principles

1. Never show stale UI - Loading states only when actually loading
2. Always surface errors - Users must know when something fails
3. Optimistic updates - Make the UI feel instant
4. Progressive disclosure - Use @defer to show content as available
5. Graceful degradation - Partial data is better than no data

---

Loading State Patterns

The Golden Rule

Show loading indicator ONLY when there's no data to display.

@Component({
  template: `
    @if (error()) {
      <app-error-state [error]="error()" (retry)="load()" />
    } @else if (loading() && !items().length) {
      <app-skeleton-list />
    } @else if (!items().length) {
      <app-empty-state message="No items found" />
    } @else {
      <app-item-list [items]="items()" />
    }
  `,
})
export class ItemListComponent {
  private store = inject(ItemStore);

  items = this.store.items;
  loading = this.store.loading;
  error = this.store.error;
}

Loading State Decision Tree

Is there an error?
  → Yes: Show error state with retry option
  → No: Continue

Is it loading AND we have no data?
  → Yes: Show loading indicator (spinner/skeleton)
  → No: Continue

Do we have data?
  → Yes, with items: Show the data
  → Yes, but empty: Show empty state
  → No: Show loading (fallback)

Skeleton vs Spinner

Use Skeleton When	Use Spinner When
Known content shape	Unknown content shape
List/card layouts	Modal actions
Initial page load	Button submissions
Content placeholders	Inline operations

---

Control Flow Patterns

@if/@else for Conditional Rendering

@if (user(); as user) {
<span>Welcome, {{ user.name }}</span>
} @else if (loading()) {
<app-spinner size="small" />
} @else {
<a routerLink="/login">Sign In</a>
}