APG Patterns
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Accordion

A vertically stacked set of interactive headings that each reveal a section of content.

🤖 AI Implementation Guide

Demo

Single Expansion (Default)

Only one panel can be expanded at a time. Opening a new panel closes the previously open one.

An accordion is a vertically stacked set of interactive headings that each reveal a section of content. They are commonly used to reduce the need to scroll when presenting multiple sections of content on a single page.

Use accordions when you need to organize content into collapsible sections. This helps reduce visual clutter while keeping information accessible. They are particularly useful for FAQs, settings panels, and navigation menus.

Accordions must be keyboard accessible and properly announce their expanded/collapsed state to screen readers. Each header should be a proper heading element, and the panel should be associated with its header via aria-controls and aria-labelledby.

Multiple Expansion

Multiple panels can be expanded simultaneously using the allowMultiple prop.

Content for section one. With allowMultiple enabled, multiple sections can be open at the same time.

Content for section two. Try opening this while section one is still open.

Content for section three. All three sections can be expanded simultaneously.

With Disabled Items

Individual accordion items can be disabled. Keyboard navigation automatically skips disabled items.

This section can be expanded and collapsed normally.

This content is not accessible because the section is disabled.

This section can also be expanded. Notice that arrow key navigation skips the disabled section.

Accessibility Features

WAI-ARIA Roles

Role Target Element Description
heading Header wrapper (h2-h6) Contains the accordion trigger button
button Header trigger Interactive element that toggles panel visibility
region Panel (optional) Content area associated with header (omit for 6+ panels)

WAI-ARIA Accordion Pattern (opens in new tab)

WAI-ARIA Properties

Attribute Target Values Required Configuration
aria-level heading 2 - 6 Yes headingLevel prop
aria-controls button ID reference to associated panel Yes Auto-generated
aria-labelledby region (panel) ID reference to header button Yes (if region used) Auto-generated

WAI-ARIA States

aria-expanded

Indicates whether the accordion panel is expanded or collapsed.

Target button element
Values true | false
Required Yes
Change Trigger Click, Enter, Space
Reference aria-expanded (opens in new tab)

aria-disabled

Indicates whether the accordion header is disabled.

Target button element
Values true | false
Required No (only when disabled)
Reference aria-disabled (opens in new tab)

Keyboard Support

Key Action
Tab Move focus to the next focusable element
Space / Enter Toggle the expansion of the focused accordion header
Arrow Down Move focus to the next accordion header (optional)
Arrow Up Move focus to the previous accordion header (optional)
Home Move focus to the first accordion header (optional)
End Move focus to the last accordion header (optional)

Arrow key navigation is optional but recommended. Focus does not wrap around at the end of the list.

Source Code

Accordion.vue
<template>
  <div :class="`apg-accordion ${className}`.trim()">
    <div v-for="item in items" :key="item.id" :class="getItemClass(item)">
      <component :is="`h${headingLevel}`" class="apg-accordion-header">
        <button
          :ref="(el) => setButtonRef(item.id, el)"
          type="button"
          :id="`${instanceId}-header-${item.id}`"
          :aria-expanded="isExpanded(item.id)"
          :aria-controls="`${instanceId}-panel-${item.id}`"
          :aria-disabled="item.disabled || undefined"
          :disabled="item.disabled"
          :class="getTriggerClass(item)"
          @click="handleToggle(item.id)"
          @keydown="handleKeyDown($event, item.id)"
        >
          <span class="apg-accordion-trigger-content">{{ item.header }}</span>
          <span :class="getIconClass(item)" aria-hidden="true">
            <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
              <polyline points="6 9 12 15 18 9" />
            </svg>
          </span>
        </button>
      </component>
      <div
        :role="useRegion ? 'region' : undefined"
        :id="`${instanceId}-panel-${item.id}`"
        :aria-labelledby="useRegion ? `${instanceId}-header-${item.id}` : undefined"
        :class="getPanelClass(item)"
      >
        <div class="apg-accordion-panel-content">
          <div v-if="item.content" v-html="item.content" />
          <slot v-else :name="item.id" />
        </div>
      </div>
    </div>
  </div>
</template>

<script setup lang="ts">
/**
 * APG Accordion Pattern - Vue Implementation
 *
 * A vertically stacked set of interactive headings that each reveal a section of content.
 *
 * @see https://www.w3.org/WAI/ARIA/apg/patterns/accordion/
 */
import { ref, computed } from 'vue';

/**
 * Accordion item configuration
 */
export interface AccordionItem {
  /** Unique identifier for the item */
  id: string;
  /** Content displayed in the accordion header button */
  header: string;
  /** Content displayed in the collapsible panel (HTML string) */
  content?: string;
  /** When true, the item cannot be expanded/collapsed */
  disabled?: boolean;
  /** When true, the panel is expanded on initial render */
  defaultExpanded?: boolean;
}

/**
 * Props for the Accordion component
 *
 * @example
 * ```vue
 * <Accordion
 *   :items="[
 *     { id: 'section1', header: 'Section 1', content: 'Content 1', defaultExpanded: true },
 *     { id: 'section2', header: 'Section 2', content: 'Content 2' },
 *   ]"
 *   :heading-level="3"
 *   :allow-multiple="false"
 *   @expanded-change="(ids) => console.log('Expanded:', ids)"
 * />
 * ```
 */
export interface AccordionProps {
  /** Array of accordion items to display */
  items: AccordionItem[];
  /** Allow multiple panels to be expanded simultaneously @default false */
  allowMultiple?: boolean;
  /** Heading level for accessibility (h2-h6) @default 3 */
  headingLevel?: 2 | 3 | 4 | 5 | 6;
  /** Enable arrow key navigation @default true */
  enableArrowKeys?: boolean;
  /** Additional CSS class @default "" */
  className?: string;
}

const props = withDefaults(defineProps<AccordionProps>(), {
  allowMultiple: false,
  headingLevel: 3,
  enableArrowKeys: true,
  className: '',
});

const emit = defineEmits<{
  expandedChange: [expandedIds: string[]];
}>();

// Initialize with defaultExpanded items immediately
const getInitialExpandedIds = () => {
  return props.items
    .filter((item) => item.defaultExpanded && !item.disabled)
    .map((item) => item.id);
};

const expandedIds = ref<string[]>(getInitialExpandedIds());
const instanceId = ref(`accordion-${Math.random().toString(36).substr(2, 9)}`);
const buttonRefs = ref<Record<string, HTMLButtonElement>>({});

const setButtonRef = (id: string, el: unknown) => {
  if (el instanceof HTMLButtonElement) {
    buttonRefs.value[id] = el;
  }
};

const availableItems = computed(() => props.items.filter((item) => !item.disabled));

// Use role="region" only for 6 or fewer panels (APG recommendation)
const useRegion = computed(() => props.items.length <= 6);

const isExpanded = (itemId: string) => expandedIds.value.includes(itemId);

const getItemClass = (item: AccordionItem) => {
  const classes = ['apg-accordion-item'];
  if (isExpanded(item.id)) classes.push('apg-accordion-item--expanded');
  if (item.disabled) classes.push('apg-accordion-item--disabled');
  return classes.join(' ');
};

const getTriggerClass = (item: AccordionItem) => {
  const classes = ['apg-accordion-trigger'];
  if (isExpanded(item.id)) classes.push('apg-accordion-trigger--expanded');
  return classes.join(' ');
};

const getIconClass = (item: AccordionItem) => {
  const classes = ['apg-accordion-icon'];
  if (isExpanded(item.id)) classes.push('apg-accordion-icon--expanded');
  return classes.join(' ');
};

const getPanelClass = (item: AccordionItem) => {
  return `apg-accordion-panel ${isExpanded(item.id) ? 'apg-accordion-panel--expanded' : 'apg-accordion-panel--collapsed'}`;
};

const handleToggle = (itemId: string) => {
  const item = props.items.find((i) => i.id === itemId);
  if (item?.disabled) return;

  const isCurrentlyExpanded = expandedIds.value.includes(itemId);

  if (isCurrentlyExpanded) {
    expandedIds.value = expandedIds.value.filter((id) => id !== itemId);
  } else {
    if (props.allowMultiple) {
      expandedIds.value = [...expandedIds.value, itemId];
    } else {
      expandedIds.value = [itemId];
    }
  }

  emit('expandedChange', expandedIds.value);
};

const handleKeyDown = (event: KeyboardEvent, currentItemId: string) => {
  if (!props.enableArrowKeys) return;

  const currentIndex = availableItems.value.findIndex((item) => item.id === currentItemId);
  if (currentIndex === -1) return;

  let newIndex = currentIndex;
  let shouldPreventDefault = false;

  switch (event.key) {
    case 'ArrowDown':
      // Move to next, but don't wrap (APG compliant)
      if (currentIndex < availableItems.value.length - 1) {
        newIndex = currentIndex + 1;
      }
      shouldPreventDefault = true;
      break;

    case 'ArrowUp':
      // Move to previous, but don't wrap (APG compliant)
      if (currentIndex > 0) {
        newIndex = currentIndex - 1;
      }
      shouldPreventDefault = true;
      break;

    case 'Home':
      newIndex = 0;
      shouldPreventDefault = true;
      break;

    case 'End':
      newIndex = availableItems.value.length - 1;
      shouldPreventDefault = true;
      break;
  }

  if (shouldPreventDefault) {
    event.preventDefault();
    if (newIndex !== currentIndex) {
      const newItem = availableItems.value[newIndex];
      if (newItem && buttonRefs.value[newItem.id]) {
        buttonRefs.value[newItem.id].focus();
      }
    }
  }
};
</script>

Usage

Example
<script setup>
import Accordion from './Accordion.vue';

const items = [
  {
    id: 'section1',
    header: 'First Section',
    content: 'Content for the first section...',
    defaultExpanded: true,
  },
  {
    id: 'section2',
    header: 'Second Section',
    content: 'Content for the second section...',
  },
];
</script>

<template>
  <Accordion
    :items="items"
    :heading-level="3"
    :allow-multiple="false"
    @expanded-change="(ids) => console.log('Expanded:', ids)"
  />
</template>

API

Props

Prop Type Default Description
items AccordionItem[] required Array of accordion items
allowMultiple boolean false Allow multiple panels to be expanded
headingLevel 2 | 3 | 4 | 5 | 6 3 Heading level for accessibility
enableArrowKeys boolean true Enable arrow key navigation

Events

Event Payload Description
expanded-change string[] Emitted when the expanded panels change

AccordionItem Interface

Types
interface AccordionItem {
  id: string;
  header: string;
  content?: string;
  disabled?: boolean;
  defaultExpanded?: boolean;
}

Testing

Tests verify APG compliance across keyboard interaction, ARIA attributes, and accessibility requirements.

Test Categories

High Priority: APG Keyboard Interaction

Test Description
Enter key Expands/collapses the focused panel
Space key Expands/collapses the focused panel
ArrowDown Moves focus to next header
ArrowUp Moves focus to previous header
Home Moves focus to first header
End Moves focus to last header
No loop Focus stops at edges (no wrapping)
Disabled skip Skips disabled headers during navigation

High Priority: APG ARIA Attributes

Test Description
aria-expanded Header button reflects expand/collapse state
aria-controls Header references its panel via aria-controls
aria-labelledby Panel references its header via aria-labelledby
role="region" Panel has region role (6 or fewer panels)
No region (7+) Panel omits region role when 7+ panels
aria-disabled Disabled items have aria-disabled="true"

High Priority: Heading Structure

Test Description
headingLevel prop Uses correct heading element (h2, h3, etc.)

Medium Priority: Accessibility

Test Description
axe violations No WCAG 2.1 AA violations (via jest-axe)

Low Priority: Props & Behavior

Test Description
allowMultiple Controls single vs. multiple expansion
defaultExpanded Sets initial expansion state
className Custom classes are applied

Testing Tools

See testing-strategy.md (opens in new tab) for full documentation.

Accordion.test.vue.ts
import { render, screen } from '@testing-library/vue';
import userEvent from '@testing-library/user-event';
import { axe } from 'jest-axe';
import { describe, expect, it, vi } from 'vitest';
import Accordion from './Accordion.vue';
import type { AccordionItem } from './Accordion.vue';

// テスト用のアコーディオンデータ
const defaultItems: AccordionItem[] = [
  { id: 'section1', header: 'Section 1', content: 'Content 1' },
  { id: 'section2', header: 'Section 2', content: 'Content 2' },
  { id: 'section3', header: 'Section 3', content: 'Content 3' },
];

const itemsWithDisabled: AccordionItem[] = [
  { id: 'section1', header: 'Section 1', content: 'Content 1' },
  { id: 'section2', header: 'Section 2', content: 'Content 2', disabled: true },
  { id: 'section3', header: 'Section 3', content: 'Content 3' },
];

const itemsWithDefaultExpanded: AccordionItem[] = [
  { id: 'section1', header: 'Section 1', content: 'Content 1', defaultExpanded: true },
  { id: 'section2', header: 'Section 2', content: 'Content 2' },
  { id: 'section3', header: 'Section 3', content: 'Content 3' },
];

// 7個以上のアイテム(region role テスト用)
const manyItems: AccordionItem[] = Array.from({ length: 7 }, (_, i) => ({
  id: `section${i + 1}`,
  header: `Section ${i + 1}`,
  content: `Content ${i + 1}`,
}));

describe('Accordion (Vue)', () => {
  // 🔴 High Priority: APG 準拠の核心
  describe('APG: キーボード操作', () => {
    it('Enter でパネルを開閉する', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button = screen.getByRole('button', { name: 'Section 1' });
      button.focus();

      expect(button).toHaveAttribute('aria-expanded', 'false');
      await user.keyboard('{Enter}');
      expect(button).toHaveAttribute('aria-expanded', 'true');
      await user.keyboard('{Enter}');
      expect(button).toHaveAttribute('aria-expanded', 'false');
    });

    it('Space でパネルを開閉する', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button = screen.getByRole('button', { name: 'Section 1' });
      button.focus();

      expect(button).toHaveAttribute('aria-expanded', 'false');
      await user.keyboard(' ');
      expect(button).toHaveAttribute('aria-expanded', 'true');
    });

    it('ArrowDown で次のヘッダーにフォーカス移動', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      button1.focus();

      await user.keyboard('{ArrowDown}');

      const button2 = screen.getByRole('button', { name: 'Section 2' });
      expect(button2).toHaveFocus();
    });

    it('ArrowUp で前のヘッダーにフォーカス移動', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button2 = screen.getByRole('button', { name: 'Section 2' });
      button2.focus();

      await user.keyboard('{ArrowUp}');

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      expect(button1).toHaveFocus();
    });

    it('ArrowDown で最後のヘッダーにいる場合、移動しない(ループなし)', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button3 = screen.getByRole('button', { name: 'Section 3' });
      button3.focus();

      await user.keyboard('{ArrowDown}');

      expect(button3).toHaveFocus();
    });

    it('ArrowUp で最初のヘッダーにいる場合、移動しない(ループなし)', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      button1.focus();

      await user.keyboard('{ArrowUp}');

      expect(button1).toHaveFocus();
    });

    it('Home で最初のヘッダーに移動', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button3 = screen.getByRole('button', { name: 'Section 3' });
      button3.focus();

      await user.keyboard('{Home}');

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      expect(button1).toHaveFocus();
    });

    it('End で最後のヘッダーに移動', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      button1.focus();

      await user.keyboard('{End}');

      const button3 = screen.getByRole('button', { name: 'Section 3' });
      expect(button3).toHaveFocus();
    });

    it('disabled ヘッダーをスキップして移動', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: itemsWithDisabled } });

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      button1.focus();

      await user.keyboard('{ArrowDown}');

      const button3 = screen.getByRole('button', { name: 'Section 3' });
      expect(button3).toHaveFocus();
    });

    it('enableArrowKeys=false で矢印キーナビゲーション無効', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems, enableArrowKeys: false } });

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      button1.focus();

      await user.keyboard('{ArrowDown}');

      expect(button1).toHaveFocus();
    });
  });

  describe('APG: ARIA 属性', () => {
    it('ヘッダーボタンが aria-expanded を持つ', () => {
      render(Accordion, { props: { items: defaultItems } });
      const buttons = screen.getAllByRole('button');

      buttons.forEach((button) => {
        expect(button).toHaveAttribute('aria-expanded');
      });
    });

    it('開いたパネルで aria-expanded="true"', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button = screen.getByRole('button', { name: 'Section 1' });
      await user.click(button);

      expect(button).toHaveAttribute('aria-expanded', 'true');
    });

    it('閉じたパネルで aria-expanded="false"', () => {
      render(Accordion, { props: { items: defaultItems } });
      const button = screen.getByRole('button', { name: 'Section 1' });

      expect(button).toHaveAttribute('aria-expanded', 'false');
    });

    it('ヘッダーの aria-controls がパネル id と一致', () => {
      render(Accordion, { props: { items: defaultItems } });
      const button = screen.getByRole('button', { name: 'Section 1' });
      const ariaControls = button.getAttribute('aria-controls');

      expect(ariaControls).toBeTruthy();
      expect(document.getElementById(ariaControls!)).toBeInTheDocument();
    });

    it('6個以下のパネルで role="region" を持つ', () => {
      render(Accordion, { props: { items: defaultItems } });
      const regions = screen.getAllByRole('region');

      expect(regions).toHaveLength(3);
    });

    it('7個以上のパネルで role="region" を持たない', () => {
      render(Accordion, { props: { items: manyItems } });
      const regions = screen.queryAllByRole('region');

      expect(regions).toHaveLength(0);
    });

    it('パネルの aria-labelledby がヘッダー id と一致', () => {
      render(Accordion, { props: { items: defaultItems } });
      const button = screen.getByRole('button', { name: 'Section 1' });
      const regions = screen.getAllByRole('region');

      expect(regions[0]).toHaveAttribute('aria-labelledby', button.id);
    });

    it('disabled 項目が aria-disabled="true" を持つ', () => {
      render(Accordion, { props: { items: itemsWithDisabled } });
      const disabledButton = screen.getByRole('button', { name: 'Section 2' });

      expect(disabledButton).toHaveAttribute('aria-disabled', 'true');
    });
  });

  describe('APG: 見出し構造', () => {
    it('headingLevel=3 で h3 要素を使用', () => {
      render(Accordion, { props: { items: defaultItems, headingLevel: 3 } });
      const headings = document.querySelectorAll('h3');

      expect(headings).toHaveLength(3);
    });

    it('headingLevel=2 で h2 要素を使用', () => {
      render(Accordion, { props: { items: defaultItems, headingLevel: 2 } });
      const headings = document.querySelectorAll('h2');

      expect(headings).toHaveLength(3);
    });
  });

  // 🟡 Medium Priority: アクセシビリティ検証
  describe('アクセシビリティ', () => {
    it('axe による WCAG 2.1 AA 違反がない', async () => {
      const { container } = render(Accordion, { props: { items: defaultItems } });
      const results = await axe(container);
      expect(results).toHaveNoViolations();
    });
  });

  describe('Props', () => {
    it('defaultExpanded で初期展開状態を指定できる', () => {
      render(Accordion, { props: { items: itemsWithDefaultExpanded } });
      const button = screen.getByRole('button', { name: 'Section 1' });

      expect(button).toHaveAttribute('aria-expanded', 'true');
    });

    it('allowMultiple=false で1つのみ展開(デフォルト)', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems } });

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      const button2 = screen.getByRole('button', { name: 'Section 2' });

      await user.click(button1);
      expect(button1).toHaveAttribute('aria-expanded', 'true');

      await user.click(button2);
      expect(button1).toHaveAttribute('aria-expanded', 'false');
      expect(button2).toHaveAttribute('aria-expanded', 'true');
    });

    it('allowMultiple=true で複数展開可能', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: defaultItems, allowMultiple: true } });

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      const button2 = screen.getByRole('button', { name: 'Section 2' });

      await user.click(button1);
      await user.click(button2);

      expect(button1).toHaveAttribute('aria-expanded', 'true');
      expect(button2).toHaveAttribute('aria-expanded', 'true');
    });

    it('@expandedChange が展開状態変化時に発火する', async () => {
      const handleExpandedChange = vi.fn();
      const user = userEvent.setup();
      render(Accordion, {
        props: { items: defaultItems, onExpandedChange: handleExpandedChange },
      });

      await user.click(screen.getByRole('button', { name: 'Section 1' }));

      expect(handleExpandedChange).toHaveBeenCalledWith(['section1']);
    });
  });

  describe('異常系', () => {
    it('disabled 項目はクリックで開閉しない', async () => {
      const user = userEvent.setup();
      render(Accordion, { props: { items: itemsWithDisabled } });

      const disabledButton = screen.getByRole('button', { name: 'Section 2' });

      expect(disabledButton).toHaveAttribute('aria-expanded', 'false');
      await user.click(disabledButton);
      expect(disabledButton).toHaveAttribute('aria-expanded', 'false');
    });

    it('disabled かつ defaultExpanded の項目は展開されない', () => {
      const items: AccordionItem[] = [
        {
          id: 'section1',
          header: 'Section 1',
          content: 'Content 1',
          disabled: true,
          defaultExpanded: true,
        },
      ];
      render(Accordion, { props: { items } });

      const button = screen.getByRole('button', { name: 'Section 1' });
      expect(button).toHaveAttribute('aria-expanded', 'false');
    });
  });
});

Resources