Best Practices

Accessibility in Angular

The web is used by a wide variety of people, including those who have visual or motor impairments. A variety of assistive technologies are available that make it much easier for these groups to interact with web-based software applications. Also, designing an application to be more accessible generally improves the user experience for all users.

For an in-depth introduction to issues and techniques for designing accessible applications, see Google's web.dev Learn Accessibility course.

This page discusses best practices for designing Angular applications that work well for all users, including those who rely on assistive technologies.

Accessibility attributes

Building accessible web experience often involves setting Accessible Rich Internet Applications (ARIA) attributes to provide semantic meaning where it might otherwise be missing. Use attribute binding template syntax to control the values of accessibility-related attributes.

When binding to ARIA attributes in Angular, you must use the attr. prefix. The ARIA specification depends specifically on HTML attributes rather than properties of DOM elements.

      
<!-- Use attr. when binding to an ARIA attribute --><button [attr.aria-label]="myActionLabel">…</button>

Note: This syntax is only necessary for attribute bindings. Static ARIA attributes require no extra syntax.

      
<!-- Static ARIA attributes require no extra syntax --><button aria-label="Save document">…</button>

HELPFUL: By convention, HTML attributes use lowercase names (tabindex), while properties use camelCase names (tabIndex).

See the Binding syntax guide for more background on the difference between attributes and properties.

Angular UI components

The Angular Material library, which is maintained by the Angular team, is a suite of reusable UI components that aims to be fully accessible. The Component Development Kit (CDK) includes the a11y package that provides tools to support various areas of accessibility. For example:

  • LiveAnnouncer is used to announce messages for screen-reader users using an aria-live region. See the W3C documentation for more information on aria-live regions.

  • The cdkTrapFocus directive traps Tab-key focus within an element. Use it to create accessible experience for components such as modal dialogs, where focus must be constrained.

For full details of these and other tools, see the Angular CDK accessibility overview.

Augmenting native elements

Native HTML elements capture several standard interaction patterns that are important to accessibility. When authoring Angular components, you should re-use these native elements directly when possible, rather than re-implementing well-supported behaviors.

For example, instead of creating a custom element for a new variety of button, create a component that uses an attribute selector with a native <button> element. This most commonly applies to <button> and <a>, but can be used with many other types of element.

You can see examples of this pattern in Angular Material: MatButton, MatTabNav, and MatTable.

Using containers for native elements

Sometimes using the appropriate native element requires a container element. For example, the native <input> element cannot have children, so any custom text entry components need to wrap an <input> with extra elements. By just including <input> in your custom component's template, it's impossible for your component's users to set arbitrary properties and attributes to the <input> element. Instead, create a container component that uses content projection to include the native control in the component's API.

You can see MatFormField as an example of this pattern.

Case study: Building a custom progress bar

The following example shows how to make a progress bar accessible by using host binding to control accessibility-related attributes.

  • The component defines an accessibility-enabled element with both the standard HTML attribute role, and ARIA attributes. The ARIA attribute aria-valuenow is bound to the user's input.
  • In the template, the aria-label attribute ensures that the control is accessible to screen readers.
      
1import {Component, Input} from '@angular/core';23/**4 * Example progressbar component.5 */6@Component({7  selector: 'app-example-progressbar',8  template: '<div class="bar" [style.width.%]="value"></div>',9  styleUrls: ['./progress-bar.component.css'],10  host: {11    // Sets the role for this component to "progressbar"12    role: 'progressbar',1314    // Sets the minimum and maximum values for the progressbar role.15    'aria-valuemin': '0',16    'aria-valuemax': '100',1718    // Binding that updates the current value of the progressbar.19    '[attr.aria-valuenow]': 'value',20  },21})22export class ExampleProgressbarComponent {23  /** Current value of the progressbar. */24  @Input() value = 0;25}2627

    
      
1<h1>Accessibility Example</h1>2<label for="progress-value">3  Enter an example progress value4  <input id="progress-value" type="number" min="0" max="100"5      [value]="progress" (input)="setProgress($event)">6</label>78<!-- The user of the progressbar sets an aria-label to communicate what the progress means. -->9<app-example-progressbar [value]="progress" aria-label="Example of a progress bar">10</app-example-progressbar>1112

Routing

Focus management after navigation

Tracking and controlling focus in a UI is an important consideration in designing for accessibility. When using Angular routing, you should decide where page focus goes upon navigation.

To avoid relying solely on visual cues, you need to make sure your routing code updates focus after page navigation. Use the NavigationEnd event from the Router service to know when to update focus.

The following example shows how to find and focus the main content header in the DOM after navigation.

      
router.events.pipe(filter(e => e instanceof NavigationEnd)).subscribe(() => {  const mainHeader = document.querySelector('#main-content-header')  if (mainHeader) {    mainHeader.focus();  }});

In a real application, the element that receives focus depends on your specific application structure and layout. The focused element should put users in a position to immediately move into the main content that has just been routed into view. You should avoid situations where focus returns to the body element after a route change.

CSS classes applied to active RouterLink elements, such as RouterLinkActive, provide a visual cue to identify the active link. Unfortunately, a visual cue doesn't help blind or visually impaired users. Applying the aria-current attribute to the element can help identify the active link. For more information, see Mozilla Developer Network (MDN) aria-current).

The RouterLinkActive directive provides the ariaCurrentWhenActive input which sets the aria-current to a specified value when the link becomes active.

The following example shows how to apply the active-page class to active links as well as setting their aria-current attribute to "page" when they are active:

      
<nav>  <a routerLink="home"      routerLinkActive="active-page"      ariaCurrentWhenActive="page">    Home  </a>  <a routerLink="about"      routerLinkActive="active-page"      ariaCurrentWhenActive="page">    About  </a>  <a routerLink="shop"      routerLinkActive="active-page"      ariaCurrentWhenActive="page">    Shop  </a></nav>

More information

Books

  • "A Web for Everyone: Designing Accessible User Experiences," Sarah Horton and Whitney Quesenbery
  • "Inclusive Design Patterns," Heydon Pickering