Dependency Injection — Angular Technical Interview Questions & Answers

Dependency Injection

Dependency Injection

  • DI means Angular creates the object and passes it in the constructor. constructor(private marks: MarksService). You don’t call new. Providers tell Angular how to make it.
  • providedIn: 'root' → one singleton. providedIn a component → new instance for that component tree. Use root for MarksService. Use component provider only when you want isolation.
  • Trap: circular inject (A needs B needs A). Split a third helper. Another trap: forgetting to provide a non-root service and getting NullInjectorError.

Technical Interview Tip: constructor inject + providedIn. NullInjectorError meaning.

Code Examples for Dependency Injection

Dependency Injection — working example

import { Injectable } from "@angular/core";

@Injectable({ providedIn: "root" })
export class UserService {
  getName() {
    return "Asha";
  }
}

Dependency Injection — services hold shared logic; Angular DI injects them into components.

How to Explain Dependency Injection to an Interviewer

What is dependency injection in Angular?

Framework creates deps constructor(private svc: …)

What is NullInjectorError?

Service not provided