Reactでコンポーネントの誤用を防ぐ！制約付き設計の実践例と応用

import React from 'react';
import PropTypes from 'prop-types';

const UserProfile = ({ name, age, isPremiumMember }) => {
  return (
    <div>
      <h1>{name}</h1>
      <p>Age: {age}</p>
      <p>Premium Member: {isPremiumMember ? 'Yes' : 'No'}</p>
    </div>
  );
};

UserProfile.propTypes = {
  name: PropTypes.string.isRequired, // 必須の文字列型
  age: PropTypes.number,            // オプショナルな数値型
  isPremiumMember: PropTypes.bool   // オプショナルな真偽値型
};

export default UserProfile;

UserProfile.propTypes = {
  hobbies: PropTypes.arrayOf(PropTypes.string), // 文字列の配列
  address: PropTypes.shape({
    city: PropTypes.string.isRequired,
    zipCode: PropTypes.number
  })
};

import React from 'react';

// Propsの型定義
type UserProfileProps = {
  name: string;
  age?: number; // オプショナルなプロパティ
  isPremiumMember: boolean;
};

// コンポーネント定義
const UserProfile: React.FC<UserProfileProps> = ({ name, age, isPremiumMember }) => {
  return (
    <div>
      <h1>{name}</h1>
      <p>Age: {age ?? 'Not specified'}</p>
      <p>Premium Member: {isPremiumMember ? 'Yes' : 'No'}</p>
    </div>
  );
};

export default UserProfile;

type Address = {
  city: string;
  zipCode?: number;
};

type UserProfileProps = {
  name: string;
  address: Address;
};

type ListProps<T> = {
  items: T[];
  renderItem: (item: T) => JSX.Element;
};

const List = <T,>({ items, renderItem }: ListProps<T>) => (
  <ul>{items.map(renderItem)}</ul>
);

type Status = 'active' | 'inactive' | 'banned';

type User = {
  name: string;
  status: Status;
};

import React, { createContext, useContext, useState } from 'react';

// Contextの作成
const ThemeContext = createContext();

// プロバイダーコンポーネント
const ThemeProvider = ({ children }) => {
  const [theme, setTheme] = useState('light');

  return (
    <ThemeContext.Provider value={{ theme, setTheme }}>
      {children}
    </ThemeContext.Provider>
  );
};

// コンシューマーコンポーネント
const ThemeSwitcher = () => {
  const { theme, setTheme } = useContext(ThemeContext);

  return (
    <div>
      <p>Current Theme: {theme}</p>
      <button onClick={() => setTheme(theme === 'light' ? 'dark' : 'light')}>
        Toggle Theme
      </button>
    </div>
  );
};

// アプリケーション全体で利用
const App = () => (
  <ThemeProvider>
    <ThemeSwitcher />
  </ThemeProvider>
);

export default App;

const AuthContext = createContext();

const AuthProvider = ({ children }) => {
  const [user, setUser] = useState(null);

  return (
    <AuthContext.Provider value={{ user, setUser }}>
      {children}
    </AuthContext.Provider>
  );
};

const useAuth = () => useContext(AuthContext);

import { useState } from 'react';

// カスタムフック
const useForm = (initialValues) => {
  const [values, setValues] = useState(initialValues);

  const handleChange = (event) => {
    const { name, value } = event.target;
    setValues({
      ...values,
      [name]: value,
    });
  };

  return { values, handleChange };
};

export default useForm;

import React from 'react';
import useForm from './useForm';

const LoginForm = () => {
  const { values, handleChange } = useForm({ username: '', password: '' });

  const handleSubmit = (event) => {
    event.preventDefault();
    console.log(values);
  };

  return (
    <form onSubmit={handleSubmit}>
      <input
        name="username"
        value={values.username}
        onChange={handleChange}
        placeholder="Username"
      />
      <input
        name="password"
        type="password"
        value={values.password}
        onChange={handleChange}
        placeholder="Password"
      />
      <button type="submit">Login</button>
    </form>
  );
};

export default LoginForm;

import { useState, useEffect } from 'react';

const useFetch = (url) => {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch(url);
        if (!response.ok) {
          throw new Error('Failed to fetch');
        }
        const result = await response.json();
        setData(result);
      } catch (err) {
        setError(err.message);
      } finally {
        setLoading(false);
      }
    };

    fetchData();
  }, [url]);

  return { data, loading, error };
};

export default useFetch;

import React from 'react';
import useFetch from './useFetch';

const UserList = () => {
  const { data, loading, error } = useFetch('https://api.example.com/users');

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error: {error}</p>;

  return (
    <ul>
      {data.map((user) => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
};

export default UserList;

type ButtonVariant = 'primary' | 'secondary';

type ButtonProps = {
  variant: ButtonVariant;
  onClick: () => void;
  children: React.ReactNode;
};

const Button: React.FC<ButtonProps> = ({ variant, onClick, children }) => {
  const styles = variant === 'primary' ? 'btn-primary' : 'btn-secondary';

  return (
    <button className={styles} onClick={onClick}>
      {children}
    </button>
  );
};

export default Button;

type AuthWrapperProps = {
  isAuthenticated: boolean;
  children: React.ReactNode;
};

const AuthWrapper: React.FC<AuthWrapperProps> = ({ isAuthenticated, children }) => {
  if (!isAuthenticated) {
    return <p>Access Denied. Please log in.</p>;
  }

  return <>{children}</>;
};

export default AuthWrapper;

import { useContext, createContext } from 'react';

type Theme = 'light' | 'dark';

type ThemeContextType = {
  theme: Theme;
  toggleTheme: () => void;
};

const ThemeContext = createContext<ThemeContextType | undefined>(undefined);

export const ThemeProvider: React.FC<{ children: React.ReactNode }> = ({ children }) => {
  const [theme, setTheme] = React.useState<Theme>('light');

  const toggleTheme = () => {
    setTheme((prev) => (prev === 'light' ? 'dark' : 'light'));
  };

  return (
    <ThemeContext.Provider value={{ theme, toggleTheme }}>
      {children}
    </ThemeContext.Provider>
  );
};

export const useTheme = (): ThemeContextType => {
  const context = useContext(ThemeContext);
  if (!context) {
    throw new Error('useTheme must be used within a ThemeProvider');
  }
  return context;
};

const ParentComponent: React.FC<{ children: React.ReactNode }> = ({ children }) => {
  return <div className="parent">{children}</div>;
};

type ChildProps = {
  parentOnly: boolean;
};

const ChildComponent: React.FC<ChildProps> = ({ parentOnly }) => {
  if (!parentOnly) {
    throw new Error('ChildComponent must be used within ParentComponent');
  }
  return <p>I am a child component</p>;
};

// 使用例
const App = () => (
  <ParentComponent>
    <ChildComponent parentOnly={true} />
  </ParentComponent>
);

console.log(props);
console.log(state);

// 修正例
<MyComponent propName="Expected String" />;

// 型チェック
MyComponent.propTypes = {
  propName: PropTypes.string.isRequired,
};

MyComponent.defaultProps = {
  optionalProp: 'Default Value',
};

// 誤り
const theme = useTheme(); // ThemeProvider外で呼び出し

// 修正例
<ThemeProvider>
  <ChildComponent />
</ThemeProvider>

test('renders with correct props', () => {
  render(<MyComponent propName="Test Value" />);
  expect(screen.getByText('Test Value')).toBeInTheDocument();
});

const Button: React.FC<ButtonProps> = ({ variant, size, children }) => {
  const className = `btn-${variant} btn-${size}`;
  return <button className={className}>{children}</button>;
};

const MemoizedComponent = React.memo(({ data }) => {
  return <div>{data}</div>;
});

const LazyComponent = React.lazy(() => import('./HeavyComponent'));

<Suspense fallback={<div>Loading...</div>}>
  <LazyComponent />
</Suspense>;