Accessibility

The a11y package provides a number of tools to improve accessibility, described below.

ListKeyManager

ListKeyManager manages the active option in a list of items based on keyboard interaction. Intended to be used with components that correspond to a role="menu" or role="listbox" pattern.

link Basic usage

Any component that uses a ListKeyManager will generally do three things:

• Create a @ViewChildren query for the options being managed.
• Initialize the ListKeyManager, passing in the options.
• Forward keyboard events from the managed component to the ListKeyManager.

Each option should implement the ListKeyManagerOption interface:

interface ListKeyManagerOption {
  disabled?: boolean;
  getLabel?(): string;
}

link Wrapping

Navigation through options can be made to wrap via the withWrap method

this.keyManager = new FocusKeyManager(...).withWrap();

link Types of key managers

There are two varieties of ListKeyManager, FocusKeyManager and ActiveDescendantKeyManager.

link FocusKeyManager

Used when options will directly receive browser focus. Each item managed must implement the FocusableOption interface:

interface FocusableOption extends ListKeyManagerOption {
  focus(): void;
}

link ActiveDescendantKeyManager

Used when options will be marked as active via aria-activedescendant. Each item managed must implement the Highlightable interface:

interface Highlightable extends ListKeyManagerOption {
  setActiveStyles(): void;
  setInactiveStyles(): void;
}

Each item must also have an ID bound to the listbox's or menu's aria-activedescendant.

FocusTrap

The cdkTrapFocus directive traps Tab key focus within an element. This is intended to be used to create accessible experience for components like modal dialogs, where focus must be constrained.

This directive is declared in A11yModule.

link Example

<div class="my-inner-dialog-content" cdkTrapFocus>
  <!-- Tab and Shift + Tab will not leave this element. -->
</div>

This directive will not prevent focus from moving out of the trapped region due to mouse interaction.

link Regions

Regions can be declared explicitly with an initial focus element by using the cdkFocusRegionStart, cdkFocusRegionEnd and cdkFocusInitial DOM attributes. cdkFocusInitial specifies the element that will receive focus upon initialization of the region. cdkFocusRegionStart and cdkFocusRegionEnd define the region within which focus will be trapped. When using the tab key, focus will move through this region and wrap around on either end.

For example:

<a mat-list-item routerLink cdkFocusRegionStart>Focus region start</a>
<a mat-list-item routerLink>Link</a>
<a mat-list-item routerLink cdkFocusInitial>Initially focused</a>
<a mat-list-item routerLink cdkFocusRegionEnd>Focus region end</a>

InteractivityChecker

InteractivityChecker is used to check the interactivity of an element, capturing disabled, visible, tabbable, and focusable states for accessibility purposes. See the API docs for more details.

LiveAnnouncer

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

link Example

@Component({...})
export class MyComponent {

 constructor(liveAnnouncer: LiveAnnouncer) {
   liveAnnouncer.announce("Hey Google");
 }
}

FocusMonitor

The FocusMonitor is an injectable service that can be used to listen for changes in the focus state of an element. It's more powerful than just listening for focus or blur events because it tells you how the element was focused (via mouse, keyboard, touch, or programmatically). It also allows listening for focus on descendant elements if desired.

To listen for focus changes on an element, use the monitor method which takes an element to monitor and an optional boolean flag checkChildren. Passing true for checkChildren will tell the FocusMonitor to consider the element focused if any of its descendants are focused. This option defaults to false if not specified. The monitor method will return an Observable that emits the FocusOrigin whenever the focus state changes. The FocusOrigin will be one of the following:

• 'mouse' indicates the element was focused with the mouse
• 'keyboard' indicates the element was focused with the keyboard
• 'touch' indicates the element was focused by touching on a touchscreen
• 'program' indicates the element was focused programmatically
• null indicates the element was blurred

In addition to emitting on the observable, the FocusMonitor will automatically apply CSS classes to the element when focused. It will add .cdk-focused if the element is focused and will further add .cdk-${origin}-focused (with ${origin} being mouse, keyboard, touch, or program) to indicate how the element was focused.

Note: currently the FocusMonitor emits on the observable outside of the Angular zone. Therefore if you markForCheck in the subscription you must put yourself back in the Angular zone.

focusMonitor.monitor(el).subscribe(origin => this.ngZone.run(() => /* ... */ ));

Any element that is monitored by calling monitor should eventually be unmonitored by calling stopMonitoring with the same element.

It is possible to falsify the FocusOrigin when setting the focus programmatically by using the focusVia method of FocusMonitor. This method accepts an element to focus and the FocusOrigin to use. If the element being focused is currently being monitored by the FocusMonitor it will report the FocusOrigin that was passed in. If the element is not currently being monitored it will just be focused like normal.

link cdkMonitorElementFocus and cdkMonitorSubtreeFocus

For convenience, the CDK also provides two directives that allow for easily monitoring an element. cdkMonitorElementFocus is the equivalent of calling monitor on the host element with checkChildren set to false. cdkMonitorSubtreeFocus is the equivalent of calling monitor on the host element with checkChildren set to true. Each of these directives has an @Output() cdkFocusChange that will emit the new FocusOrigin whenever it changes.

Styling utilities

The CDK a11y package comes with a set of CSS styles that can be used when building accessible components. To take advantage of them, you have to include the styles in your global stylesheet. If you're using Material together with the CDK, these styles have been included for you already.

@import '~@angular/cdk/text-field/text-field';

@include cdk-a11y();

link Hiding elements, while keeping them available for screen readers

By default, screen readers and other assistive technology will skip elements that have display: none, visibility: hidden etc. In some cases you may need to visually hide an element, while keeping it available for assistive technology. You can do so using the cdk-visually-hidden class:

<div class="custom-checkbox">
  <input type="checkbox" class="cdk-visually-hidden">
</div>

link Targeting high contrast users

The a11y package offers a mixin that allows you to target users that have the Windows high contrast mode turned on, via a media query. To target high contrast users, you can wrap your styles with the cdk-high-contrast mixin:

button {
  @include cdk-high-contrast {
    outline: solid 1px;
  }
}