angular-di

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• SKILL.md
• di-patterns.md · references/

SKILL.md (first lines)

# Angular Dependency Injection

Configure and use dependency injection in Angular v20+ with `inject()` and providers.

## Basic Injection

### Using inject()

Prefer `inject()` over constructor injection:

```typescript
import { Component, inject } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { User } from './user.service';

@Component({
  selector: 'app-user-list',
  template: `...`,
})
export class UserList {
  // Inject dependencies
  private http = inject(HttpClient);
  private userService = inject(User);
  
  // Can use immediately
  users = this.userService.getUsers();
}
```

### Injectable Services

```typescript
import { Injectable, inject, signal } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Injectable({
  providedIn: 'root', // Singleton at root level
})
export class User {
  private http = inject(HttpClient);
  
  private users = signal<User[]>([]);
  readonly users$ = this.users.asReadonly();
  
  async loadUsers() {
    const users = await firstValueFrom(
      this.http.get<User[]>('/api/users')
    );
    this.users.set(users);
  }
}
```

## Provider Scopes

### Root Level (Singleton)

```typescript
// Recommended: providedIn
@Injectable({
  providedIn: 'root',
})
export class Auth {}

// Alternative: in app.config.ts
export const appConfig: ApplicationConfig = {
  providers: [
    Auth,
  ],
};
```

### Component Level (Instance per Component)

```typescript
@Component({
  selector: 'app-editor',
  providers: [EditorState], // New instance for each component
  template: `...`,
})
export class Editor {
  private editorState = inject(EditorState);
}
```

### Route Level

```typescript
export const routes: Routes = [
  {
    path: 'admin',
    providers: [Admin], // Shared within this route tree
    children: [
      { path: '', component: AdminDashboard },
      { path: 'users', component: AdminUsers },
    ],
  },
];
```

## Injection Tokens

### Creating Tokens

```typescript
import { InjectionToken } from '@angular/core';

// Simple value token
export const API_URL = new InjectionToken<string>('API_URL');

// Object token
export interface AppConfig {
  apiUrl: string;
  features: {
    darkMode: boolean;
    analytics: boolean;
  };
}

From manu14357/zskills, MIT.

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