TypeScriptのセキュリティアーキテクチャ：保護システム型安全性

            function calculateDiscount(price, discountRate) {
 return price * discountRate;
}

let price = '100'; // Oops, this is a string
let discount = 0.1;
let finalPrice = calculateDiscount(price, discount); // Runtime error (or unexpected result)
console.log(finalPrice);
            

              
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            function calculateDiscount(price: number, discountRate: number): number {
 return price * discountRate;
}

let price: string = '100'; // TypeScript error: Type 'string' is not assignable to type 'number'
let discount: number = 0.1;
let finalPrice = calculateDiscount(price, discount); // Compilation error
console.log(finalPrice);
            

              
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            interface UserProfile {
  id: number;
  username: string;
  email: string;
  country: string; // e.g., 'US', 'GB', 'JP'
  phoneNumber?: string; // Optional, use string for international formats
  dateOfBirth?: Date; // Optional
  address?: {
    street: string;
    city: string;
    postalCode: string;
    country: string; // Redundant, but shown for clarity
  };
}

function updateUserProfile(user: UserProfile, updates: Partial): UserProfile {
  // Implementation to update user profile based on updates
  return { ...user, ...updates }; // Example: Simple merge with spread syntax
}

let existingUser: UserProfile = {
  id: 123,
  username: 'john.doe',
  email: 'john.doe@example.com',
  country: 'US',
  phoneNumber: '+1-555-123-4567',
  dateOfBirth: new Date('1990-01-15'),
  address: {
    street: '123 Main St',
    city: 'Anytown',
    postalCode: '12345',
    country: 'US'
  }
};

// Example Updates:
let updateProfile = {
  username: 'john.doe.updated',
  address: {
    city: 'Springfield',
  }
}

let updatedUser = updateUserProfile(existingUser, updateProfile);
console.log(updatedUser);

            

              
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            // ESLint rule to flag unused variables:
let unusedVariable: string = 'This variable is unused'; // ESLint will flag this

// ESLint rule to prevent potentially null references:
let potentiallyNull: string | null = null;
// if (potentiallyNull.length > 0) { // ESLint would flag this, potential for runtime error
// }

            

              
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            interface AuthenticationRequest {
  username: string;
  password: string;
}

interface AuthenticationResponse {
  success: boolean;
  token?: string; // JWT token (optional)
  error?: string;
}

async function authenticateUser(request: AuthenticationRequest): Promise {
  // Validate input (e.g., username/password length, format)
  if (request.username.length < 3 || request.password.length < 8) {
    return { success: false, error: 'Invalid credentials' };
  }

  // Security note: Always hash passwords before storing/comparing them
  // Example (using a hypothetical hashing function):
  // const hashedPassword = await hashPassword(request.password);

  // Authentication Logic (e.g., check against a database)
  let isValid = true; // Placeholder, replace with actual authentication
  if (isValid) {
    const token = generateJwtToken(request.username); // Secure token generation
    return { success: true, token };
  } else {
    return { success: false, error: 'Invalid credentials' };
  }
}

            

              
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            // Before Refactoring (less type safety)
function fetchData(url: string, callback: (data: any) => void) {
  fetch(url)
    .then(response => response.json())
    .then(data => callback(data))
    .catch(error => console.error('Error fetching data:', error));
}

// After Refactoring (more type safety)
interface UserData {
  id: number;
  name: string;
  email: string;
}

function fetchDataTyped(url: string, callback: (data: UserData) => void) {
  fetch(url)
    .then(response => response.json())
    .then((data: any) => {
      // Type assertion if the response doesn't directly conform to UserData
      //  e.g.,  const userData: UserData = data as UserData;
      // or more robust error handling
      if (data && typeof data === 'object' && 'id' in data && 'name' in data && 'email' in data) {
        callback(data as UserData);
      } else {
         console.error('Invalid data format received'); // Improved error handling
      }
    })
    .catch(error => console.error('Error fetching data:', error));
}

// Usage Example:
fetchDataTyped('/api/users/1', (userData) => {
  console.log('User data:', userData.name); // Type-safe access to userData properties
});

            

              
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            // Input validation example with a validation library like 'validator'
import validator from 'validator';

interface UserRegistration {
  email: string;
  password: string;
}

function validateRegistration(data: UserRegistration): boolean {
  if (!validator.isEmail(data.email)) {
    console.error('Invalid email address');
    return false;
  }
  if (data.password.length < 8) {
    console.error('Password must be at least 8 characters');
    return false;
  }
  return true;
}

const registrationData: UserRegistration = {
  email: 'invalid-email',
  password: 'short'
};

if (validateRegistration(registrationData)) {
  // Proceed with user registration
  console.log('Registration data is valid');
}

            

              
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            // Secure password storage with hashing (example, NOT production-ready)
import *s bcrypt from 'bcrypt'; // npm install bcrypt

async function hashPassword(password: string): Promise {
  const saltRounds = 10; // Adjust salt rounds for security, must be >= 10
  const salt = await bcrypt.genSalt(saltRounds);
  const hashedPassword = await bcrypt.hash(password, salt);
  return hashedPassword;
}

// Example of storing in an environment variable (Node.js)
// const apiKey = process.env.API_KEY || 'default-api-key';  // Use .env files with caution

// Example of protecting API keys and secrets:
// - Never commit API keys/secrets directly in source code.
// - Store API keys in environment variables (.env files - be cautious with those or configuration files, depending on the project setup)
// - Utilize secure secrets management services (e.g., AWS Secrets Manager, Azure Key Vault, Google Cloud Secret Manager).

            

              
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            // Proper error handling example
async function fetchData(url: string): Promise {
  try {
    const response = await fetch(url);
    if (!response.ok) {
      throw new Error(`HTTP error! status: ${response.status}`);
    }
    return await response.json();
  } catch (error: any) {
    console.error('Error fetching data:', error);
    // Log the error for debugging.
    //  example:  logError(error, 'fetchData');  // (use a logging library)
    //  In production, avoid revealing details about underlying implementation details.
    throw new Error('An error occurred while fetching data. Please try again later.'); // User-friendly error
  }
}

// Example usage:
fetchData('/api/data')
  .then(data => {
    // Process data
    console.log('Data:', data);
  })
  .catch(error => {
    // Handle errors
    console.error('Error in main flow:', error.message); // User-friendly message
  });

            

              
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            // Securing asynchronous operations with async/await and try/catch
async function processData(data: any) {
  try {
    // Simulate an async operation (e.g., database write)
    await new Promise(resolve => setTimeout(resolve, 1000)); // Simulate a delay
    console.log('Data processed:', data);
  } catch (error) {
    // Handle errors that occur during the asynchronous operation.
    console.error('Error processing data:', error);
    // Implement retry logic or alert the user, logging is crucial.
  } finally {
    // Perform cleanup actions, like closing database connections
    // always implement the finally block to ensure consistent state
    console.log('Cleanup actions');
  }
}

// Example of data processing
processData({ message: 'Hello, World!' });

            

              
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            // Using generics for type safety in a data repository
interface DataRepository {
  getData(id: number): Promise;
  createData(item: T): Promise;
  updateData(id: number, item: Partial): Promise; // allow partial updates
  deleteData(id: number): Promise;
}

// Example: User Repository
interface User {
  id: number;
  name: string;
  email: string;
}

class UserRepository implements DataRepository {
  // Implementation details for data access (e.g., database calls)
  async getData(id: number): Promise {
    // ... (Retrieve user data)
    return undefined; // Replace with an implementation
  }

  async createData(item: User): Promise {
    // ... (Create a new user)
    return item;
  }

  async updateData(id: number, item: Partial): Promise {
    // ... (Update user)
    return undefined;
  }

  async deleteData(id: number): Promise {
    // ... (Delete user)
    return false;
  }
}

// Usage Example:
const userRepository = new UserRepository();
userRepository.getData(123).then(user => {
  if (user) {
    console.log('User data:', user);
  }
});

            

              
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            {
  "compilerOptions": {
    "target": "ES2020", // Or a later version
    "module": "CommonJS", // Or "ESNext", depending on your project
    "strict": true, // Enable strict type checking
    "esModuleInterop": true,
    "skipLibCheck": true, // Skip type checking of declaration files (.d.ts) for libraries to improve compilation time
    "forceConsistentCasingInFileNames": true, // For case sensitivity across file systems
    "noImplicitAny": true, //  More strict control of the any type
    "noImplicitThis": true,  // For this context errors
    "strictNullChecks": true,  // Requires null and undefined to be handled explicitly.
    "strictFunctionTypes": true,
    "strictBindCallApply": true,
    "baseUrl": ".",
    "paths": {  // Configure module resolution paths (optional)
      "*": ["./src/*"]
    }
  },
  "include": ["src/**/*"]
}

            

              
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            // .eslintrc.js (example)
module.exports = {
  parser: '@typescript-eslint/parser',
  extends: [
    'plugin:@typescript-eslint/recommended', // Includes TypeScript-specific rules
    'prettier',
    'plugin:prettier/recommended' // Integrates with Prettier for code formatting
  ],
  plugins: [
    '@typescript-eslint'
  ],
  parserOptions: {
    ecmaVersion: 2020,
    sourceType: 'module'
  },
  rules: {
    // Security-related rules:
    '@typescript-eslint/no-explicit-any': 'warn',  // Prevents the use of 'any' (can be too permissive)
    '@typescript-eslint/no-unused-vars': 'warn', // Checks for unused variables, including local and global, preventing potential vulnerabilities.
    'no-console': 'warn',  // Prevents unintentional use of console.log/debug statements in production code.
    '@typescript-eslint/no-floating-promises': 'error', // Prevents potential promise leaks
    // ... other rules specific to your project
  }
};

            

              
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            // Using internationalization libraries like 'Intl' API in Javascript
// Example: Displaying currency
const amount = 1234.56;
const options: Intl.NumberFormatOptions = {
  style: 'currency',
  currency: 'USD'
};
const formatter = new Intl.NumberFormat('en-US', options);
const formattedUSD = formatter.format(amount);  // $1,234.56

const optionsJPY: Intl.NumberFormatOptions = {
  style: 'currency',
  currency: 'JPY'
};
const formatterJPY = new Intl.NumberFormat('ja-JP', optionsJPY);
const formattedJPY = formatterJPY.format(amount); // ¥1,235

            

              
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            // Example: obtaining user consent (simplistic)
interface UserConsent {
  marketingEmails: boolean;
  dataAnalytics: boolean;
}

function getUserConsent(): UserConsent {
    //  Implementation to obtain user preferences
    //  Typically, present a user interface (e.g., a checkbox form).
    return {
        marketingEmails: true,  // Assume the user consents by default for this example
        dataAnalytics: false    // assume user doesn't opt-in for analytics
    };
}

function processUserData(consent: UserConsent, userData: any) {
  if (consent.marketingEmails) {
    // Send marketing emails based on consent.
    console.log('Sending marketing emails', userData);
  }
  if (consent.dataAnalytics) {
    //  Process data analytics.
    console.log('Analyzing user data', userData);
  } else {
    //  Avoid analytics processing, implement data minimization
    console.log('Skipping analytics (no consent)');
  }
}

            

              
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