From 382fc9358751f660040228efbb44a088c2e03466 Mon Sep 17 00:00:00 2001
From: Olson <bela.olson@nih.gov>
Date: Mon, 13 Apr 2026 17:00:07 -0400
Subject: [PATCH] (#28) Implement Dropdown/Select component

* Adds Dropdown and Dropdown Option components with NCIDS usa-select classes
* Support configurable options
* Includes unit tests
* Adds Storybook documentation

Closes #28
---
 .storybook/preview.scss                       |  2 +
 .../ncids/Dropdown/Dropdown.stories.tsx       | 57 ++++++++++++
 .../ncids/Dropdown/Dropdown.test.tsx          | 91 +++++++++++++++++++
 src/components/ncids/Dropdown/Dropdown.tsx    | 67 ++++++++++++++
 src/components/ncids/Dropdown/index.ts        |  2 +
 src/components/ncids/index.ts                 |  2 +
 6 files changed, 221 insertions(+)
 create mode 100644 src/components/ncids/Dropdown/Dropdown.stories.tsx
 create mode 100644 src/components/ncids/Dropdown/Dropdown.test.tsx
 create mode 100644 src/components/ncids/Dropdown/Dropdown.tsx
 create mode 100644 src/components/ncids/Dropdown/index.ts

diff --git a/.storybook/preview.scss b/.storybook/preview.scss
index 92e0b24..af60bd1 100644
--- a/.storybook/preview.scss
+++ b/.storybook/preview.scss
@@ -8,3 +8,5 @@
 @forward 'usa-pagination';
 @forward 'usa-icon';
 @forward 'usa-collection';
+@forward 'usa-select';
+@forward 'usa-combo-box';
diff --git a/src/components/ncids/Dropdown/Dropdown.stories.tsx b/src/components/ncids/Dropdown/Dropdown.stories.tsx
new file mode 100644
index 0000000..30d0a2f
--- /dev/null
+++ b/src/components/ncids/Dropdown/Dropdown.stories.tsx
@@ -0,0 +1,57 @@
+import type { Meta, StoryObj } from '@storybook/react';
+import { fn } from '@storybook/test';
+import React from 'react';
+
+import { Dropdown } from './Dropdown';
+
+const meta: Meta<typeof Dropdown> = {
+	title: 'NCIDS/Dropdown',
+	component: Dropdown,
+	tags: ['autodocs'],
+	argTypes: {
+		className: {
+			control: 'text',
+			description: 'Additional CSS classes on the list',
+		},
+	},
+};
+
+export default meta;
+type Story = StoryObj<typeof Dropdown>;
+
+export const Default: Story = {
+	args: {
+		id: 'default-dropdown',
+		name: 'default-dropdown',
+		options: [
+			{ label: '20', value: 20 },
+			{ label: '50', value: 50 },
+			{ label: '100', value: 100 },
+		],
+		onChange: fn(),
+	},
+};
+
+export const WithResultsPerPageText: Story = {
+	name: 'With Results Per Page Text',
+	render: (args) => {
+		return (
+			<div style={{ display: 'flex', alignItems: 'center', gap: '0.5rem' }}>
+				<span>Show</span>
+				<Dropdown {...args} style={{ width: '70px' }} />
+				<span>results per page</span>
+			</div>
+		);
+	},
+	args: {
+		id: 'results-per-page',
+		name: 'results-per-page',
+		ariaLabel: 'Select option',
+		options: [
+			{ label: '20', value: 20 },
+			{ label: '50', value: 50 },
+			{ label: '100', value: 100 },
+		],
+		onChange: fn(),
+	},
+};
diff --git a/src/components/ncids/Dropdown/Dropdown.test.tsx b/src/components/ncids/Dropdown/Dropdown.test.tsx
new file mode 100644
index 0000000..8c122f7
--- /dev/null
+++ b/src/components/ncids/Dropdown/Dropdown.test.tsx
@@ -0,0 +1,91 @@
+import React from 'react';
+import { cleanup, render, screen } from '@testing-library/react';
+import { axe } from 'vitest-axe';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import userEvent from '@testing-library/user-event';
+
+import { Dropdown } from './Dropdown';
+
+describe('<Dropdown />', () => {
+	afterEach(() => {
+		cleanup();
+	});
+
+	it('should render options', () => {
+		render(
+			<Dropdown
+				id="test"
+				name="test"
+				ariaLabel="Select option"
+				options={[
+					{ label: '20', value: 20 },
+					{ label: '30', value: 30 },
+					{ label: '50', value: 50 },
+					{ label: '100', value: 100 },
+				]}
+			/>
+		);
+
+		expect(screen.getByRole('option', { name: '20' })).toBeInTheDocument();
+		expect(screen.getByRole('option', { name: '30' })).toBeInTheDocument();
+		expect(screen.getByRole('option', { name: '50' })).toBeInTheDocument();
+		expect(screen.getByRole('option', { name: '100' })).toBeInTheDocument();
+	});
+
+	it('should render a select with usa-select class', () => {
+		const { container } = render(
+			<Dropdown
+				id="test"
+				name="test"
+				ariaLabel="Select option"
+				options={[
+					{ label: '20', value: '20' },
+					{ label: '30', value: '30' },
+				]}
+			/>
+		);
+		const select = container.querySelector('select');
+		expect(select).toHaveClass('usa-select');
+	});
+
+	it('should call onChange when selection changes', async () => {
+		const user = userEvent.setup();
+		const handleChange = vi.fn();
+
+		render(
+			<Dropdown
+				id="test"
+				name="test"
+				onChange={handleChange}
+				ariaLabel="Select option"
+				options={[
+					{ label: 'Twenty', value: 20 },
+					{ label: 'Thirty', value: 30 },
+				]}
+			/>
+		);
+
+		const select = screen.getByRole('combobox');
+		await user.selectOptions(select, '20');
+
+		expect(handleChange).toHaveBeenCalledTimes(1);
+	});
+
+	it('should have no accessibility violations', async () => {
+		const handleChange = vi.fn();
+		const { container } = render(
+			<Dropdown
+				id="test"
+				name="test"
+				ariaLabel="Select option"
+				onChange={handleChange}
+				options={[
+					{ label: 'Twenty', value: 20 },
+					{ label: 'Thirty', value: 30 },
+				]}
+			/>
+		);
+		const results = await axe(container);
+		expect(results).toHaveNoViolations();
+	});
+});
diff --git a/src/components/ncids/Dropdown/Dropdown.tsx b/src/components/ncids/Dropdown/Dropdown.tsx
new file mode 100644
index 0000000..1764223
--- /dev/null
+++ b/src/components/ncids/Dropdown/Dropdown.tsx
@@ -0,0 +1,67 @@
+import React from 'react';
+
+export interface DropdownOptionProps {
+	/** Option label */
+	label: string;
+	/** Additional CSS classes on the <option>. */
+	className?: string;
+	/** Value of the option */
+	value: string | number;
+}
+
+export const DropdownOption: React.FC<DropdownOptionProps> = ({
+	label,
+	className,
+	value,
+}) => {
+	return (
+		<option key={`option_${value}`} value={value} className={className}>
+			{label}
+		</option>
+	);
+};
+
+export interface DropdownProps
+	extends React.SelectHTMLAttributes<HTMLSelectElement> {
+	/** Dropdown list ID */
+	id: string;
+	/** Name for the dropdown list */
+	name: string;
+	/** Additional CSS classes on the <select>. */
+	className?: string;
+	/** Array of options */
+	options: DropdownOptionProps[];
+	/** Aria label on the <select> */
+	ariaLabel: string;
+	/** Callback fired when an option is selected */
+	onChange?: (event: React.ChangeEvent<HTMLSelectElement>) => void;
+}
+
+export const Dropdown: React.FC<DropdownProps> = ({
+	id,
+	name,
+	options,
+	className,
+	ariaLabel,
+	onChange,
+	...rest
+}) => {
+	const classes = ['usa-select', className || ''].filter(Boolean).join(' ');
+
+	return (
+		<select
+			className={classes}
+			name={name}
+			id={id}
+			aria-label={ariaLabel}
+			onChange={onChange}
+			{...rest}
+		>
+			{options.map((opt) => (
+				<DropdownOption key={`option_${opt.value}`} {...opt} />
+			))}
+		</select>
+	);
+};
+
+export default Dropdown;
diff --git a/src/components/ncids/Dropdown/index.ts b/src/components/ncids/Dropdown/index.ts
new file mode 100644
index 0000000..f30b1ed
--- /dev/null
+++ b/src/components/ncids/Dropdown/index.ts
@@ -0,0 +1,2 @@
+export { Dropdown, default } from './Dropdown';
+export type { DropdownProps } from './Dropdown';
diff --git a/src/components/ncids/index.ts b/src/components/ncids/index.ts
index 5ec3538..130d5d3 100644
--- a/src/components/ncids/index.ts
+++ b/src/components/ncids/index.ts
@@ -3,3 +3,5 @@ export { Pager } from './Pager';
 export type { PagerProps, PageChangeData } from './Pager';
 export { Collection, CollectionItem } from './Collection';
 export type { CollectionProps, CollectionItemProps } from './Collection';
+export { Dropdown } from './Dropdown';
+export type { DropdownProps } from './Dropdown';