Component Library

Component Library Building Skill

Overview

Learn to build reusable, accessible, and well-documented component libraries for React applications using modern design patterns and tools.

Learning Objectives

• Design reusable component APIs
• Implement accessible components (WCAG 2.1)
• Create component variants and compositions
• Build documentation with Storybook
• Publish and maintain npm packages

Component Design Principles

1. Flexible and Composable

// Good: Flexible API
<Card>
  <Card.Header>
    <Card.Title>Title</Card.Title>
  </Card.Header>
  <Card.Body>Content</Card.Body>
  <Card.Footer>
    <Button>Action</Button>
  </Card.Footer>
</Card>

// Bad: Rigid API
<Card title="Title" content="Content" action="Action" />

2. Accessible by Default

function Button({ children, onClick, disabled, ...props }) {
  return (
    <button
      type="button"
      onClick={onClick}
      disabled={disabled}
      aria-disabled={disabled}
      {...props}
    >
      {children}
    </button>
  );
}

Essential Components

Button Component

const Button = forwardRef(({
  children,
  variant = 'primary',
  size = 'md',
  disabled = false,
  loading = false,
  leftIcon,
  rightIcon,
  ...props
}, ref) => {
  return (
    <button
      ref={ref}
      className={`btn btn-${variant} btn-${size}`}
      disabled={disabled || loading}
      aria-busy={loading}
      {...props}
    >
      {leftIcon && <span className="btn-icon-left">{leftIcon}</span>}
      {loading ? <Spinner size="sm" /> : children}
      {rightIcon && <span className="btn-icon-right">{rightIcon}</span>}
    </button>
  );
});

Button.displayName = 'Button';

Input Component

const Input = forwardRef(({
  label,
  error,
  helper,
  required,
  ...props
}, ref) => {
  const id = useId();

  return (
    <div className="input-wrapper">
      {label && (
        <label htmlFor={id}>
          {label}
          {required && <span aria-label="required">*</span>}
        </label>
      )}
      <input
        ref={ref}
        id={id}
        aria-invalid={!!error}
        aria-describedby={error ? `${id}-error` : helper ? `${id}-helper` : undefined}
        {...props}
      />
      {helper && <span id={`${id}-helper`} className="input-helper">{helper}</span>}
      {error && <span id={`${id}-error`} className="input-error" role="alert">{error}</span>}
    </div>
  );
});

Modal Component

function Modal({ isOpen, onClose, title, children }) {
  const modalRef = useRef(null);

  useEffect(() => {
    if (isOpen) {
      const previousActiveElement = document.activeElement;
      modalRef.current?.focus();

      return () => {
        previousActiveElement?.focus();
      };
    }
  }, [isOpen]);

  useOnClickOutside(modalRef, onClose);

  if (!isOpen) return null;

  return createPortal(
    <div className="modal-overlay" role="dialog" aria-modal="true" aria-labelledby="modal-title">
      <div ref={modalRef} className="modal" tabIndex={-1}>
        <div className="modal-header">
          <h2 id="modal-title">{title}</h2>
          <button onClick={onClose} aria-label="Close modal">×</button>
        </div>
        <div className="modal-body">{children}</div>
      </div>
    </div>,
    document.body
  );
}

Dropdown Component

function Dropdown({ trigger, children }) {
  const [isOpen, setIsOpen] = useState(false);
  const dropdownRef = useRef(null);

  useOnClickOutside(dropdownRef, () => setIsOpen(false));

  return (
    <div ref={dropdownRef} className="dropdown">
      <div onClick={() => setIsOpen(!isOpen)} role="button" aria-expanded={isOpen}>
        {trigger}
      </div>
      {isOpen && (
        <div className="dropdown-menu" role="menu">
          {children}
        </div>
      )}
    </div>
  );
}

function DropdownItem({ onClick, children }) {
  return (
    <div className="dropdown-item" role="menuitem" onClick={onClick} tabIndex={0}>
      {children}
    </div>
  );
}

Dropdown.Item = DropdownItem;

Compound Components Pattern

Tabs Component

const TabsContext = createContext();

function Tabs({ children, defaultTab }) {
  const [activeTab, setActiveTab] = useState(defaultTab);

  return (
    <TabsContext.Provider value={{ activeTab, setActiveTab }}>
      <div className="tabs">{children}</div>
    </TabsContext.Provider>
  );
}

function TabList({ children }) {
  return <div className="tab-list" role="tablist">{children}</div>;
}

function Tab({ id, children }) {
  const { activeTab, setActiveTab } = useContext(TabsContext);

  return (
    <button
      role="tab"
      aria-selected={activeTab === id}
      onClick={() => setActiveTab(id)}
      className={activeTab === id ? 'active' : ''}
    >
      {children}
    </button>
  );
}

function TabPanels({ children }) {
  return <div className="tab-panels">{children}</div>;
}

function TabPanel({ id, children }) {
  const { activeTab } = useContext(TabsContext);
  if (activeTab !== id) return null;

  return <div role="tabpanel">{children}</div>;
}

Tabs.List = TabList;
Tabs.Tab = Tab;
Tabs.Panels = TabPanels;
Tabs.Panel = TabPanel;

Storybook Integration

Installation

npx storybook@latest init

Button Stories

// Button.stories.jsx
import { Button } from './Button';

export default {
  title: 'Components/Button',
  component: Button,
  argTypes: {
    variant: {
      control: 'select',
      options: ['primary', 'secondary', 'danger']
    },
    size: {
      control: 'select',
      options: ['sm', 'md', 'lg']
    }
  }
};

export const Primary = {
  args: {
    variant: 'primary',
    children: 'Button'
  }
};

export const WithIcons = {
  args: {
    leftIcon: <Icon name="star" />,
    children: 'Button'
  }
};

export const Loading = {
  args: {
    loading: true,
    children: 'Loading...'
  }
};

TypeScript Support

// Button.tsx
interface ButtonProps extends React.ButtonHTMLAttributes<HTMLButtonElement> {
  variant?: 'primary' | 'secondary' | 'danger';
  size?: 'sm' | 'md' | 'lg';
  loading?: boolean;
  leftIcon?: React.ReactNode;
  rightIcon?: React.ReactNode;
}

const Button = forwardRef<HTMLButtonElement, ButtonProps>(
  ({ children, variant = 'primary', size = 'md', ...props }, ref) => {
    return (
      <button ref={ref} className={`btn btn-${variant} btn-${size}`} {...props}>
        {children}
      </button>
    );
  }
);

Publishing to npm

package.json Setup

{
  "name": "@yourname/component-library",
  "version": "1.0.0",
  "main": "dist/index.js",
  "module": "dist/index.esm.js",
  "types": "dist/index.d.ts",
  "files": ["dist"],
  "peerDependencies": {
    "react": "^18.0.0",
    "react-dom": "^18.0.0"
  }
}

Practice Projects

1. Build a complete Button component with variants 2. Create accessible Form components (Input, Select, Checkbox) 3. Implement Modal with focus trap 4. Build Dropdown with keyboard navigation 5. Create Tabs compound component 6. Implement Toast notification system 7. Build Tooltip component

Resources

• Radix UI - Headless UI components
• Headless UI - Unstyled components
• Storybook - Component documentation
• React Aria - Accessibility

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Difficulty: Intermediate to Advanced Estimated Time: 3-4 weeks Prerequisites: React Fundamentals, Component Architecture

component-library Guide