Alert
An element that displays a brief, important message in a way that attracts the user's attention without interrupting the user's task.
Demo
The Astro implementation uses a Web Component that provides a setMessage() method for updating alert content. The live region container
exists in the DOM from page load - only the content changes.
Accessibility Features
WAI-ARIA Roles
| Role | Target Element | Description |
|---|---|---|
alert | Alert container | An element that displays a brief, important message that attracts the user’s attention without interrupting their task |
Implicit ARIA Properties
| Attribute | Implicit Value | Description |
|---|---|---|
aria-live | assertive | Interrupts screen reader to announce immediately |
aria-atomic | true | Announces entire alert content, not just changed parts |
Keyboard Support
| Key | Action |
|---|---|
| Enter | Activates the dismiss button (if present) |
| Space | Activates the dismiss button (if present) |
- Screen readers detect changes to live regions by observing DOM mutations inside them. If the live region itself is added dynamically, some screen readers may not announce the content reliably.
Focus Management
| Event | Behavior |
|---|---|
| Alert must NOT move focus | Alerts are non-modal and should not interrupt user workflow by stealing focus |
| Alert container is not focusable | The alert element should not have tabindex or receive keyboard focus |
| Dismiss button is focusable | If present, the dismiss button can be reached via Tab navigation |
Implementation Notes
<!-- Container always in DOM -->
<div role="alert">
<!-- Content added dynamically -->
<span>Your changes have been saved.</span>
</div>
Announcement Behavior:
- Page load content: NOT announced
- Dynamic changes: ANNOUNCED immediately
- aria-live="assertive": interrupts current speech
Alert vs Status:
┌─────────────┬──────────────────────┐
│ role="alert"│ role="status" │
├─────────────┼──────────────────────┤
│ assertive │ polite │
│ interrupts │ waits for pause │
│ urgent info │ non-urgent updates │
└─────────────┴──────────────────────┘
Alert component structure and announcement behavior
Use Alert
- The message is informational and doesn’t require user action
- User workflow should NOT be interrupted
- Focus should remain on the current task
Use Alert Dialog (role=“alertdialog”)
- The message requires immediate user response
- User must acknowledge or take action before continuing
- Focus should move to the dialog (modal behavior)
Important Notes
- The live region container (role=“alert”) must exist in the DOM from page load. Do NOT dynamically add/remove the container itself. Only the content inside the container should change dynamically.
References
Source Code
---
import InfoIcon from 'lucide-static/icons/info.svg';
import CircleCheckIcon from 'lucide-static/icons/circle-check.svg';
import AlertTriangleIcon from 'lucide-static/icons/triangle-alert.svg';
import OctagonAlertIcon from 'lucide-static/icons/octagon-alert.svg';
import XIcon from 'lucide-static/icons/x.svg';
import { type AlertVariant, variantStyles as sharedVariantStyles } from './alert-config';
export type { AlertVariant };
export interface Props {
/**
* Alert message content.
* Changes to this prop trigger screen reader announcements.
*/
message?: string;
/**
* Alert variant for visual styling.
* Does NOT affect ARIA - all variants use role="alert"
*/
variant?: AlertVariant;
/**
* Custom ID for the alert container.
* Useful for SSR/hydration consistency.
*/
id?: string;
/**
* Whether to show dismiss button.
* Note: Manual dismiss only - NO auto-dismiss per WCAG 2.2.3
*/
dismissible?: boolean;
/**
* Additional class name for the alert container
*/
class?: string;
}
const {
message = '',
variant = 'info',
id,
dismissible = false,
class: className = '',
} = Astro.props;
const alertId = id ?? `alert-${crypto.randomUUID().slice(0, 8)}`;
const variantIcons = {
info: InfoIcon,
success: CircleCheckIcon,
warning: AlertTriangleIcon,
error: OctagonAlertIcon,
};
const IconComponent = variantIcons[variant];
const hasContent = Boolean(message);
---
<apg-alert
class:list={[
'apg-alert',
hasContent && [
'relative flex items-start gap-3 rounded-lg border px-4 py-3',
'transition-colors duration-150',
sharedVariantStyles[variant],
],
!hasContent && 'contents',
className,
]}
data-alert-id={alertId}
data-dismissible={dismissible ? 'true' : undefined}
data-variant={variant}
>
{/* Live region - contains only content for screen reader announcement */}
<div
id={alertId}
role="alert"
class:list={[hasContent && 'flex flex-1 items-start gap-3', !hasContent && 'contents']}
>
{
hasContent && (
<>
<span class="apg-alert-icon mt-0.5 flex-shrink-0" aria-hidden="true">
<IconComponent class="size-5" />
</span>
<span class="apg-alert-content flex-1">{message}</span>
</>
)
}
</div>
{/* Dismiss button - outside live region to avoid SR announcing it as part of alert */}
{
hasContent && dismissible && (
<button
type="button"
class:list={[
'apg-alert-dismiss',
'-m-2 min-h-11 min-w-11 flex-shrink-0 rounded p-2',
'flex items-center justify-center',
'hover:bg-black/10 dark:hover:bg-white/10',
'focus:ring-2 focus:ring-current focus:ring-offset-2 focus:outline-none',
]}
aria-label="Dismiss alert"
>
<XIcon class="size-5" aria-hidden="true" />
</button>
)
}
</apg-alert>
<script>
import { variantStyles, variantIconSvgs, dismissIconSvg } from './alert-config';
class ApgAlert extends HTMLElement {
private alertId: string = '';
connectedCallback() {
this.alertId = this.dataset.alertId ?? '';
const dismissBtn = this.querySelector('.apg-alert-dismiss');
if (dismissBtn) {
dismissBtn.addEventListener('click', this.handleDismiss);
}
}
disconnectedCallback() {
const dismissBtn = this.querySelector('.apg-alert-dismiss');
if (dismissBtn) {
dismissBtn.removeEventListener('click', this.handleDismiss);
}
}
private handleDismiss = () => {
// Clear content but keep the alert container (live region)
const alertEl = this.querySelector(`#${this.alertId}`);
if (alertEl) {
alertEl.replaceChildren();
// Update live region classes
alertEl.classList.remove('flex-1', 'flex', 'items-start', 'gap-3');
alertEl.classList.add('contents');
}
// Update custom element display
this.className = 'apg-alert contents';
// Remove dismiss button
const existingDismissBtn = this.querySelector('.apg-alert-dismiss');
if (existingDismissBtn) {
existingDismissBtn.remove();
}
// Dispatch custom event
this.dispatchEvent(new CustomEvent('dismiss', { bubbles: true }));
};
/**
* Method to update alert message programmatically.
* The live region container remains in DOM - only content changes.
*/
setMessage(message: string, variant?: string) {
const alertEl = this.querySelector(`#${this.alertId}`);
if (!alertEl) return;
const currentVariant = (variant ??
this.dataset.variant ??
'info') as keyof typeof variantStyles;
if (message) {
// Update live region classes
alertEl.classList.remove('contents');
alertEl.classList.add('flex-1', 'flex', 'items-start', 'gap-3');
// Update custom element styles
this.classList.remove('contents');
this.className = `apg-alert relative flex items-start gap-3 px-4 py-3 rounded-lg border transition-colors duration-150 ${variantStyles[currentVariant]}`;
// Build DOM nodes safely (avoid innerHTML for user content)
const iconSpan = document.createElement('span');
iconSpan.className = 'apg-alert-icon flex-shrink-0 mt-0.5';
iconSpan.setAttribute('aria-hidden', 'true');
iconSpan.innerHTML = variantIconSvgs[currentVariant]; // Safe: hardcoded SVG
const contentSpan = document.createElement('span');
contentSpan.className = 'apg-alert-content flex-1';
contentSpan.textContent = message; // Safe: uses textContent
// Update live region content (icon + message only)
alertEl.replaceChildren(iconSpan, contentSpan);
// Remove existing dismiss button if any
const existingDismissBtn = this.querySelector('.apg-alert-dismiss');
if (existingDismissBtn) {
existingDismissBtn.remove();
}
// Add dismiss button outside live region
if (this.dataset.dismissible === 'true') {
const dismissBtn = document.createElement('button');
dismissBtn.type = 'button';
dismissBtn.className =
'apg-alert-dismiss flex-shrink-0 min-w-11 min-h-11 p-2 -m-2 rounded flex items-center justify-center hover:bg-black/10 dark:hover:bg-white/10 focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-current';
dismissBtn.setAttribute('aria-label', 'Dismiss alert');
dismissBtn.innerHTML = dismissIconSvg; // Safe: hardcoded SVG
dismissBtn.addEventListener('click', this.handleDismiss);
this.appendChild(dismissBtn);
}
} else {
alertEl.replaceChildren();
// Update live region classes
alertEl.classList.remove('flex-1', 'flex', 'items-start', 'gap-3');
alertEl.classList.add('contents');
// Update custom element display
this.className = 'apg-alert contents';
// Remove dismiss button
const existingDismissBtn = this.querySelector('.apg-alert-dismiss');
if (existingDismissBtn) {
existingDismissBtn.remove();
}
}
}
}
customElements.define('apg-alert', ApgAlert);
</script> Usage
---
import Alert from './Alert.astro';
---
<!-- IMPORTANT: Alert container is always in DOM -->
<Alert
id="my-alert"
variant="info"
dismissible
/>
<button onclick="document.querySelector('apg-alert').setMessage('Hello!')">
Show Alert
</button>
<script>
// Listen for dismiss events
document.querySelector('apg-alert')?.addEventListener('dismiss', () => {
console.log('Alert dismissed');
});
</script> API
| Prop | Type | Default | Description |
|---|---|---|---|
message | string | '' | Initial alert message |
variant | 'info' | 'success' | 'warning' | 'error' | 'info' | Visual style variant |
dismissible | boolean | false | Show dismiss button |
id | string | auto-generated | Custom ID |
class | string | - | Additional CSS classes |
<apg-alert>) for client-side interactivity. Use setMessage(message, variant?) method to update alert message programmatically. Custom Events
| Event | Detail | Description |
|---|---|---|
dismiss | - | Fired when dismiss button is clicked |
Testing
Tests verify APG compliance for live region behavior, ARIA attributes, and accessibility requirements. The Alert component uses a two-layer testing strategy.
Testing Strategy
Unit Tests (Testing Library)
Verify the component's rendered output using framework-specific testing libraries. These tests ensure correct HTML structure and ARIA attributes.
- ARIA attributes (role="alert")
- Live region container persistence in DOM
- Dismiss button accessibility
- Accessibility via jest-axe
E2E Tests (Playwright)
Verify component behavior in a real browser environment across all frameworks. These tests cover interactions and cross-framework consistency.
- ARIA structure in live browser
- Focus management (alert does NOT steal focus)
- Dismiss button keyboard interactions
- Tab navigation behavior
- axe-core accessibility scanning
- Cross-framework consistency checks
Test Categories
High Priority : APG Core Compliance (Unit + E2E)
| Test | APG Requirement |
|---|---|
| role="alert" exists | Alert container must have alert role |
| Container always in DOM | Live region must not be dynamically added/removed |
| Same container on message change | Container element identity preserved during updates |
| Focus unchanged after alert | Alert must not move keyboard focus |
| Alert not focusable | Alert container must not have tabindex |
Medium Priority : Accessibility Validation (Unit + E2E)
| Test | WCAG Requirement |
|---|---|
| No axe violations (with message) | WCAG 2.1 AA compliance |
| No axe violations (empty) | WCAG 2.1 AA compliance |
| No axe violations (dismissible) | WCAG 2.1 AA compliance |
| Dismiss button accessible name | Button has aria-label |
| Dismiss button type="button" | Prevents form submission |
Low Priority : Props & Extensibility (Unit)
| Test | Feature |
|---|---|
| variant prop changes styling | Visual customization |
| id prop sets custom ID | SSR support |
| className inheritance | Style customization |
| children for complex content | Content flexibility |
| onDismiss callback fires | Event handling |
Low Priority : Cross-framework Consistency (E2E)
| Test | Feature |
|---|---|
| All frameworks have alert | React, Vue, Svelte, Astro all render alert element |
| Same trigger buttons | All frameworks have consistent trigger buttons |
| Show alert on click | All frameworks show alert when button is clicked |
Screen Reader Testing
Automated tests verify DOM structure, but manual testing with screen readers is essential for validating actual announcement behavior.
| Screen Reader | Platform |
|---|---|
| VoiceOver | macOS / iOS |
| NVDA | Windows |
| JAWS | Windows |
| TalkBack | Android |
Verify that message changes trigger immediate announcement and that existing content on page load is NOT announced.
Testing Tools
- Vitest (opens in new tab) - Test runner for unit tests
- Testing Library (opens in new tab) - Framework-specific testing utilities (React, Vue, Svelte)
- Playwright (opens in new tab) - Browser automation for E2E tests
- axe-core/playwright (opens in new tab) - Automated accessibility testing in E2E
Running Tests
# Run all Alert tests
npm run test -- alert
# Run tests for specific framework
npm run test -- Alert.test.tsx # React
npm run test -- Alert.test.vue # Vue
npm run test -- Alert.test.svelte # Svelte See testing-strategy.md (opens in new tab) for full documentation.
Resources
- WAI-ARIA APG: Alert Pattern (opens in new tab)
- WAI-ARIA APG: Alert Dialog Pattern (opens in new tab)
- AI Implementation Guide (llm.md) (opens in new tab) - ARIA specs, keyboard support, test checklist