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AngularBeginner8 min read2026-03-01

Angular Services and Dependency Injection

Design reusable singleton and transient services in Angular using Injectable, Signals, and RxJS.

Prerequisites

  • Angular fundamentals
  • TypeScript basics

1. Generating and Providing a Singleton Service

Use providedIn: 'root' to make the service available everywhere without module declaration.

typescript
import { Injectable, signal } from '@angular/core';

export interface ToolItem {
  id: string;
  name: string;
}

@Injectable({
  providedIn: 'root'
})
export class ToolRegistryService {
  private toolsSignal = signal<ToolItem[]>([]);
  public readonly tools = this.toolsSignal.asReadonly();

  addTool(tool: ToolItem) {
    this.toolsSignal.update(list => [...list, tool]);
  }
}

Best Practices & Architecture Advice

  • Use Angular Signals (Angular 16+) for lightweight, synchronous reactive state in services.

Common Mistakes to Watch Out For

  • •Providing services in component providers array when a singleton is needed, creating multiple disjoint instances.

Frequently Asked Questions

How do I inject a service without constructor in Angular?

Use the inject() function: private toolService = inject(ToolRegistryService);

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