Q: output() vs @Output() EventEmitter — the new signal outputs?

**Target Audience:** Developers who know @Output() and EventEmitter — assumes the basics of [child-to-parent events](/interview-question/how-do-child-components-emit-events-to-parents). **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The basics of emitting an event are covered in [how child components emit events to parents](/interview-question/how-do-child-components-emit-events-to-parents); this

Q: How does two-way binding work under the hood?

**Target Audience:** Developers who use [(ngModel)] and want to know what it really is — assumes property and event binding. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The binding types themselves are covered in [the types of data binding](/interview-question/what-are-the-types-of-data-binding-in-angular); this doc goes into the compiled instructions and the runtime. Every compiled line below was copied fr

Question 1

How do child components emit events to parents?

Accepted Answer

**Target Audience:** Anyone preparing for an Angular interview who knows what a component and an input are. **Difficulty:** Easy > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The call order in section 4 and the bubbling test in section 5 were produced by compiling the examples with ngc on Angular 22.2.3 and clicking through them in jsdom. ## 1. Why This Even Matters — A Story First A child at a school play does not walk into the

Question 2

Explain how to perform unit testing on components with Signals using TestBed.

Accepted Answer

**Target Audience:** Developers moving component tests from @Input()/@Output() to the signal APIs (input(), model(), output(), computed(), effect()). **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. All results were produced by running the example spec with Angular CLI 22.2.3 (ng test --watch=false, Vitest, the default zon

Question 3

Explain what output() and outputFromObservable() are in modern Angular and how they differ from @Output().

Accepted Answer

**Target Audience:** Developers comfortable with RxJS basics who want to expose streams as component outputs. **Difficulty:** Medium to Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The plain comparison of output() with EventEmitter is in [output() versus @Output()](/interview-question/output-vs-output-eventemitter-the-new-signal-outputs); this doc focuses on the RxJS interop functions. Outputs were produced by co

Question 4

What is the role of NgRx Effects, and why do we separate side effects from reducers?

Accepted Answer

**Target Audience:** Angular developers who know the basics of the NgRx store (actions, reducers, selectors) and want to understand where HTTP calls and other side effects belong. **Difficulty:** Medium to Hard > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. The action log in section 5, the error-handling run in section 6 and the effect test in section 7 were produce

Question 5

Explain the difference between Shadow DOM, Emulated, and None View Encapsulation with compile output.

Accepted Answer

**Target Audience:** Developers who know the three encapsulation modes by name and want to see what the compiler and the runtime actually produce — comfortable with CSS selectors and attributes. **Difficulty:** Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary an interviewer expects. The compiled code in section 3 is real ngc output from Angular 22.2.3, and the runtime CSS and DOM in sections 4 and 5 were printe

Question 6

output() vs @Output() EventEmitter — the new signal outputs?

Accepted Answer

**Target Audience:** Developers who know @Output() and EventEmitter — assumes the basics of [child-to-parent events](/interview-question/how-do-child-components-emit-events-to-parents). **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The basics of emitting an event are covered in [how child components emit events to parents](/interview-question/how-do-child-components-emit-events-to-parents); this

Question 7

How do you pass data between sibling components that don't have a direct parent-child relationship?

Accepted Answer

**Target Audience:** Anyone who has passed data parent to child and now needs to share it sideways — assumes components and basic dependency injection. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Both examples were compiled with ngc on Angular 22.2.3 and run in jsdom, and both also passed the playground mode, so you can run them on this page. The RxJS comparison was run as a plain Node script. ## 1. Why Th

Question 8

How does Dependency Injection work in Angular?

Accepted Answer

**Target Audience:** Developers new to Angular, or who use services daily without knowing what builds them. Assumes TypeScript classes; no DI background needed. **Difficulty:** Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. Every output block below was produced by compiling and running the code on Angular 22.2.3; the injector chain and error messages were pri

Question 9

How does two-way binding work under the hood?

Accepted Answer

**Target Audience:** Developers who use [(ngModel)] and want to know what it really is — assumes property and event binding. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The binding types themselves are covered in [the types of data binding](/interview-question/what-are-the-types-of-data-binding-in-angular); this doc goes into the compiled instructions and the runtime. Every compiled line below was copied fr

Question 10

How do you test signal components, defer blocks, and new control flow in 2025?

Accepted Answer

**Target Audience:** Developers testing templates written with the modern Angular syntax: signals, @defer, and built-in control flow. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The title says 2025; everything here was run on the current release, Angular 22.2.3 with CLI 22.2.3 (ng test --watch=false, Vitest + jsdom, zoneless). Deep detail on signal inputs, outputs and effects is on its own page

ANGULARDECODED.

Easy

How do child components emit events to parents?

Medium

Explain how to perform unit testing on components with Signals using TestBed.

Explain what output() and outputFromObservable() are in modern Angular and how they differ from @Output().

What is the role of NgRx Effects, and why do we separate side effects from reducers?

Explain the difference between Shadow DOM, Emulated, and None View Encapsulation with compile output.

output() vs @Output() EventEmitter — the new signal outputs?

How do you pass data between sibling components that don't have a direct parent-child relationship?

How does Dependency Injection work in Angular?

How does two-way binding work under the hood?

Hard

What is the difference between AOT and JIT compilation?

What are signal inputs and model() in modern Angular?

How does compilation work under the hood in Ivy?

What is model() — two-way signal binding with model inputs?

Deferrable views — prefetch strategies and dependency isolation with @defer?

How do you dynamically create components?