Reusable Components
All Angular topicsLast updated: Jun 11, 2026
∙ Angular Topic
Reusable Components
Reusable Components teaches you how to build focused components, templates, bindings, and reusable presentation logic. This lesson uses modern Angular patterns, a focused TypeScript example, and practical production guidance.
Syntax
@Component({ selector: 'app-greeting', template: `<h2>{{ name }}</h2>` })📝 Edit Code
👁 Angular Output
💡 Edit the TypeScript example and run it to inspect the expected behavior.
Expected Output
Hello AngularLine-by-Line
| Line | Meaning |
|---|---|
import { Component } from '@angular/core'; | Angular/TypeScript line. |
@Component({ | Declares an Angular component. |
selector: 'app-greeting', | Component selector used in HTML. |
standalone: true, | Angular/TypeScript line. |
template: `<button (click)="greet()">Greet</button>`, | Defines the component template (UI). |
}) | Angular/TypeScript line. |
export class GreetingComponent { | Angular/TypeScript line. |
greet(): void { | Angular/TypeScript line. |
console.log('Hello Angular'); | Angular/TypeScript line. |
} | Angular/TypeScript line. |
} | Angular/TypeScript line. |
Real-World Uses
- 1Reusable Components is used for reusable user-interface features.
- 2In Reusable Components, the main artifact is the component or template contract.
- 3Teams apply Reusable Components to render data and react to user events declaratively.
- 4Reusable Components should be reviewed against rendered output, inputs, outputs, and user interactions.
- 5Production value from Reusable Components is visible through rendering stability and component reuse.
Common Mistakes
- 1A common Reusable Components mistake is placing business rules and subscriptions directly in presentation code.
- 2Implementing Reusable Components without defining ownership of the component or template contract.
- 3Using untyped values around Reusable Components hides invalid states and integration errors.
- 4Skipping rendered output, inputs, outputs, and user interactions leaves Reusable Components behavior unverified.
- 5Optimizing Reusable Components without measuring rendering stability and component reuse can add complexity without value.
Best Practices
- 1For Reusable Components, define the component or template contract contract before implementation.
- 2Keep Reusable Components focused on one responsibility: render data and react to user events declaratively.
- 3Represent success, empty, loading, denied, and failure states relevant to Reusable Components explicitly.
- 4Test Reusable Components through rendered output, inputs, outputs, and user interactions.
- 5Measure rendering stability and component reuse before optimizing or expanding Reusable Components.
Core idea
- 1Reusable Components centers on the component or template contract.
- 2Its purpose is to render data and react to user events declaratively.
- 3Its most common production use is reusable user-interface features.
- 4Its main design risk is placing business rules and subscriptions directly in presentation code.
How to apply it
- 1Define the component or template contract inputs, outputs, owner, and lifetime for Reusable Components.
- 2Keep Reusable Components side effects at explicit application boundaries.
- 3Model the valid and invalid states that Reusable Components can produce.
- 4Choose the smallest Angular API that fulfils the Reusable Components requirement.
Production checks
- 1Verify Reusable Components using rendered output, inputs, outputs, and user interactions.
- 2Confirm that Reusable Components does not expose private data or internal errors.
- 3Release resources owned by the component or template contract when its lifetime ends.
- 4Track rendering stability and component reuse for Reusable Components in realistic builds.
Practice path
- 1Retype the Reusable Components example and identify the component or template contract.
- 2Change one Reusable Components input and predict its observable result.
- 3Add the most relevant failure case for Reusable Components: placing business rules and subscriptions directly in presentation code.
- 4Write one test covering rendered output, inputs, outputs, and user interactions.
Quick Summary
- Reusable Components uses the component or template contract to render data and react to user events declaratively.
- Reusable Components is commonly applied to reusable user-interface features.
- The primary Reusable Components risk is placing business rules and subscriptions directly in presentation code.
- A reliable Reusable Components implementation verifies rendered output, inputs, outputs, and user interactions.
- Evaluate Reusable Components with rendering stability and component reuse.
Interview Questions
Q1. What is the purpose of Reusable Components?
Answer: It helps developers build focused components, templates, bindings, and reusable presentation logic while keeping responsibilities explicit and testable.
Q2. What is the main artifact in Reusable Components?
Answer: The main artifact is the component or template contract, which should have explicit ownership and a focused contract.
Q3. Where is Reusable Components used in real applications?
Answer: It is commonly used for reusable user-interface features.
Q4. What is a common mistake with Reusable Components?
Answer: A common mistake is placing business rules and subscriptions directly in presentation code.
Q5. How should Reusable Components be tested and evaluated?
Answer: Test rendered output, inputs, outputs, and user interactions and evaluate production behavior using rendering stability and component reuse.
Quiz
Which habit best supports Reusable Components?