Practical Guide to Writing Reusable Components in Angular
Tags: angular, tutorial, productivity, webdev
Published: 2023-08-10 15:11:19

Developing reusable components is one of the cornerstones for building well-structured and easily maintainable Angular applications. In this guide, we will delve deep into best practices for designing and implementing reusable components that promote code reusability, maintainability, and scalability.

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## Separating Responsibilities

The approach of separating responsibilities is crucial for creating reusable components. By adhering to this practice, you ensure that each component has a specific task and doesn't accumulate unnecessary functionalities. Let's explore some advanced tactics to apply this approach:

### 1. Clear and Well-Defined Interface

Start by defining a clear interface for your component. This includes comprehensively documenting which input and output properties are available, as well as how to use them. For example:

```typescript
interface CardData {
  header: string;
  content: string;
}
```

### 2. Use of Structural Directives

To keep your component focused, avoid adding complex layout structures directly to the component. Instead, use structural directives like `<ng-content>` to allow consumers to customize the layout as needed.

```html
<!-- card.component.html -->
<div class="card">
  <ng-content></ng-content>
</div>
```

### 3. The Single Responsibility Principle

A component should have a single well-defined responsibility. If the component starts accumulating too many functionalities, consider splitting those functionalities into smaller subcomponents.

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## Creating Reusable Components

Now, let's move on to the practical creation of reusable components and explore advanced techniques to make them even more versatile:

### 1. Dependency Injection

When designing components, avoid creating tight dependencies on specific services. Instead, use dependency injection to provide external services to your component. This will make the component more flexible and easy to test.

```typescript
constructor(private dataService: DataService) {}
```

### 2. Flexible Customization

Provide customization options for your component through input properties. Use attributes with sensible default values so that consumers can effortlessly customize the component.

```typescript
@Input() title = 'Default Title';
```

### 3. Event Handling

In addition to input properties, use output properties to emit events. This allows the component to notify the consumer about important actions. However, avoid excessive notifications, focusing only on significant events.

```typescript
@Output() cardClicked = new EventEmitter<CardData>();
```

### 4. Testability

Write unit and integration tests for your component. This ensures that the component works correctly in different scenarios and is crucial for long-term maintenance.

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## Advanced Usage Example

To demonstrate how to create reusable components that go beyond the basics, let's consider a list component that displays items in a flexible list format. This component can receive a `listOptions` object containing all the necessary information to configure the list.

### FlexibleListComponent

```typescript
@Component({
  selector: 'app-flexible-list',
  templateUrl: './flexible-list.component.html',
  styleUrls: ['./flexible-list.component.scss']
})
export class FlexibleListComponent {
  @Input() items: any[];
  @Input() listOptions: ListOptions;
}

export interface ListOptions {
  columnsNumber: number;
  itemTemplate?: string;
}
```

### Component Usage

```html
<app-flexible-list [items]="items" [listOptions]="listOptions"></app-flexible-list>
```
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## Conclusion

The ability to create reusable components goes beyond simply defining input and output properties. By applying advanced practices of separating responsibilities, dependency injection, flexible customization, and proper event handling, you'll be on the right path to building a solid foundation for your Angular applications.

Remember that clarity and documentation are essential when designing reusable components. Consistent practice and refining your techniques will result in robust components of high value for your teams and future projects.

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