Accessible Web Apps with Angular, TypeScript, and AllyJS
Tags: a11y, typescript, angular, webdev
Published: 2023-03-31 20:16:36

TypeScript is a powerful language that brings type safety to your JavaScript code. It has become increasingly popular in the world of web development, especially in frameworks like Angular. With the rise of accessibility concerns and the need for more inclusive web development, TypeScript A11y has become an important aspect of creating web applications.

In this article, we will explore how to use TypeScript A11y in Angular to make your applications more accessible for users with disabilities.

## What is TypeScript A11y?

TypeScript A11y is a set of APIs that provide type-safe access to the Accessibility Object Model (AOM) in TypeScript. The AOM is a new API specification that provides a way to access the accessibility tree of a web page. It allows developers to programmatically inspect and modify the accessibility properties of HTML elements.

### Using TypeScript A11y in Angular

Angular is a popular framework for building complex web applications. It provides a rich set of features that make it easy to create dynamic and interactive user interfaces. Angular also supports TypeScript out of the box, making it an ideal platform for using TypeScript A11y.

To use TypeScript A11y in Angular, you first need to install the @types/accessibility package. This package provides TypeScript definitions for the AOM API. You can install it using npm:

```
npm install @types/accessibility
```

Once you have installed the package, you can import the Accessibility interface from the @types/accessibility package and use it in your Angular components:

```typescript
import { Accessibility } from '@types/accessibility';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  constructor(private elementRef: ElementRef) {}

  ngOnInit() {
    const element = this.elementRef.nativeElement as HTMLElement;
    const aom = new Accessibility(element);
    const role = aom.getRole();
    console.log(role);
  }
}
```

In this example, we are using the Accessibility interface to get the role of an HTML element. We first create an instance of the Accessibility class by passing in the element as a parameter. We then use the getRole() method to get the role of the element and log it to the console.

## Accessibility Best Practices

When using TypeScript A11y in Angular, there are some best practices that you should follow to ensure that your application is accessible:

1. Use semantic HTML elements: Use HTML elements that have a clear and semantic meaning, such as `<nav>`, `<article>`, and `<section>`. This makes it easier for screen readers to navigate the page.

2. Provide alternative text for images: Provide descriptive alt text for images so that users with visual impairments can understand what the image represents. 
    
    ```typescript
    <img src="my-image.jpg" alt="A red sports car driving on a winding road">
    ```

4. Test with screen readers: Test your application with screen readers to ensure that it is fully accessible. There are many free screen readers available, such as `NVDA` and `VoiceOver`.

3. Use ARIA attributes: Use ARIA (Accessible Rich Internet Applications) attributes to provide additional information about the accessibility properties of an element, such as its role or state.
    - In the following example, we use ARIA attributes to provide additional information about a toggle button and its associated panel, making it accessible to users of assistive technologies.
   ```typescript
   <button [attr.aria-expanded]="isOpen ? 'true' : 'false'"
           [attr.aria-controls]="panelId"
           (click)="togglePanel()">
     Toggle Panel
   </button>

   <div [id]="panelId" [hidden]="!isOpen" [attr.aria-hidden]="!isOpen ? 'true' : 'false'">
     Panel Content
   </div>
   ```


## Conclusion

TypeScript A11y is an important aspect of creating accessible web applications. It provides a type-safe way to access the Accessibility Object Model in TypeScript, making it easier to create and maintain accessible code. By following accessibility best practices and testing your application with screen readers, you can ensure that your application is usable by all users, regardless of their abilities.