Quality assessment metrics

The Importance of Code Quality Assurance

Code quality directly impacts a project's maintainability, scalability, and stability. High-quality code reduces the likelihood of bugs, lowers maintenance costs, and improves team collaboration efficiency. In frontend projects, as business complexity increases, code quality assurance becomes particularly critical.

Core Metrics for Evaluating Code Quality

Readability

Code readability is the primary metric for assessing quality. Good naming conventions, appropriate comments, and consistent coding styles significantly enhance readability.

// Bad example
function p(d) {
  return d * 3.14;
}

// Good example
function calculatePerimeter(diameter) {
  const PI = 3.14;
  return diameter * PI;
}

Maintainability

Code should be easy to modify and extend, avoiding excessive coupling. Modular design and the Single Responsibility Principle are key.

// Bad example: High coupling
class User {
  constructor() {
    this.api = new ApiService();
  }
  
  getUser() {
    return this.api.fetch('/users');
  }
}

// Good example: Dependency injection
class User {
  constructor(apiService) {
    this.api = apiService;
  }
  
  getUser() {
    return this.api.fetch('/users');
  }
}

Performance

Frontend performance directly affects user experience. Key areas to focus on include:

• Rendering performance
• Memory usage
• Network request optimization

// Bad example: Frequent DOM operations
function updateItems(items) {
  const list = document.getElementById('list');
  list.innerHTML = '';
  items.forEach(item => {
    const li = document.createElement('li');
    li.textContent = item.name;
    list.appendChild(li);
  });
}

// Good example: Using document fragments
function updateItems(items) {
  const list = document.getElementById('list');
  const fragment = document.createDocumentFragment();
  
  items.forEach(item => {
    const li = document.createElement('li');
    li.textContent = item.name;
    fragment.appendChild(li);
  });
  
  list.innerHTML = '';
  list.appendChild(fragment);
}

Static Code Analysis Tools

ESLint

ESLint is the most popular JavaScript static analysis tool, configurable with multiple rule sets.

// .eslintrc.js
module.exports = {
  extends: ['airbnb', 'prettier'],
  rules: {
    'react/prop-types': 'off',
    'no-console': 'warn',
    'import/prefer-default-export': 'off'
  }
};

TypeScript Type Checking

TypeScript provides a powerful static type system that can detect potential issues during compilation.

interface User {
  id: number;
  name: string;
}

function getUserName(user: User): string {
  return user.name; // Type-safe
}

Test Coverage Metrics

Unit Test Coverage

Common metrics include:

• Line coverage
• Branch coverage
• Function coverage

// Jest test example
describe('calculatePerimeter', () => {
  it('should return correct perimeter', () => {
    expect(calculatePerimeter(10)).toBe(31.4);
  });
});

E2E Test Coverage

End-to-end tests focus on the completeness of user flows, commonly using tools like Cypress.

// Cypress test example
describe('Login Flow', () => {
  it('should login successfully', () => {
    cy.visit('/login');
    cy.get('#username').type('testuser');
    cy.get('#password').type('password123');
    cy.get('#submit').click();
    cy.url().should('include', '/dashboard');
  });
});

Code Complexity Metrics

Cyclomatic Complexity

A metric for measuring the logical complexity of functions. It's recommended to keep the cyclomatic complexity of a single function below 10.

// High cyclomatic complexity example
function processOrder(order) {
  if (order.isValid) {
    if (order.items.length > 0) {
      if (order.payment.isCompleted) {
        // ...more nested logic
      }
    }
  }
}

// Optimized example
function validateOrder(order) {
  return order.isValid && order.items.length > 0;
}

function processOrder(order) {
  if (!validateOrder(order)) return;
  if (!order.payment.isCompleted) return;
  // Main logic
}

Cognitive Complexity

A metric that considers the difficulty of understanding code, better reflecting actual maintenance costs than cyclomatic complexity.

Dependency Management Quality

Dependency Count

Control the number of third-party dependencies to avoid over-reliance.

# Check dependency tree
npm ls --depth=5

Dependency Versions

Regularly update dependencies to fix security vulnerabilities.

# Check outdated dependencies
npm outdated

Quality Gates in Continuous Integration

Pre-commit Hooks

Use husky to set up Git hooks for running checks before committing.

// package.json
{
  "husky": {
    "hooks": {
      "pre-commit": "lint-staged"
    }
  },
  "lint-staged": {
    "*.{js,ts}": ["eslint --fix", "prettier --write"]
  }
}

CI Pipeline Checks

Include quality checks in the CI workflow.

# .github/workflows/ci.yml
jobs:
  test:
    steps:
      - run: npm install
      - run: npm run lint
      - run: npm test
      - run: npm run build

Documentation Completeness Assessment

Code Comments

Important logic should have clear comments, but avoid over-commenting.

/**
 * Calculate discounted price for an order
 * @param basePrice - Base price
 * @param discountRate - Discount rate (0-1)
 * @returns Discounted price
 */
function calculateDiscountedPrice(basePrice: number, discountRate: number): number {
  return basePrice * (1 - discountRate);
}

API Documentation

Use Swagger or TypeDoc to generate API documentation.

/**
 * @swagger
 * /users:
 *   get:
 *     summary: Get user list
 *     responses:
 *       200:
 *         description: Successfully retrieved user list
 */
app.get('/users', (req, res) => {
  // Implementation code
});

Accessibility Metrics

WCAG Compliance

Follow the Web Content Accessibility Guidelines (WCAG) standards.

<!-- Bad example -->
<div onclick="submitForm()">Submit</div>

<!-- Good example -->
<button type="button" aria-label="Submit form" onclick="submitForm()">Submit</button>

Keyboard Navigation Testing

Ensure all functionalities can be operated via keyboard.

// Test keyboard accessibility
document.addEventListener('keydown', (e) => {
  if (e.key === 'Tab') {
    // Handle focus logic
  }
});

Security Practices Assessment

XSS Protection

Properly handle user input to prevent cross-site scripting attacks.

// Dangerous innerHTML usage
element.innerHTML = userInput;

// Safe alternative
element.textContent = userInput;

CSP Policy

Content Security Policy effectively reduces XSS risks.

<meta http-equiv="Content-Security-Policy" content="default-src 'self'">

Performance Benchmarking

Lighthouse Score

Use Lighthouse for comprehensive performance evaluation.

# Run Lighthouse test
lighthouse https://example.com --output=html --output-path=./report.html

Critical Rendering Path Optimization

Optimize first-screen rendering time.

// Lazy-load non-critical resources
import('./module').then(module => {
  module.init();
});

Code Duplication Detection

Duplicate Code Identification

Use tools like jscpd to detect code duplication.

# Detect code duplication
npx jscpd ./src

Abstracting Common Logic

Extract duplicate code into shared functions or components.

// Duplicate logic
function formatUser(user) {
  return `${user.firstName} ${user.lastName}`;
}

function formatAdmin(admin) {
  return `${admin.firstName} ${admin.lastName}`;
}

// Optimized
function formatName({ firstName, lastName }) {
  return `${firstName} ${lastName}`;
}

Error Handling Mechanisms

Error Boundaries

Use error boundaries in React applications to catch component errors.

class ErrorBoundary extends React.Component {
  state = { hasError: false };

  static getDerivedStateFromError() {
    return { hasError: true };
  }

  componentDidCatch(error, info) {
    logErrorToService(error, info);
  }

  render() {
    if (this.state.hasError) {
      return <FallbackUI />;
    }
    return this.props.children;
  }
}

Global Error Monitoring

Implement global error capture and reporting.

window.addEventListener('error', (event) => {
  trackError(event.error);
});

window.addEventListener('unhandledrejection', (event) => {
  trackError(event.reason);
});

Architecture Rationality Assessment

Component Layering

A reasonable component structure improves maintainability.

src/
├── components/      # Generic components
├── features/        # Feature modules
├── pages/           # Page components
└── utils/           # Utility functions

State Management

Choose an appropriate state management solution based on project complexity.

// Small projects using React Context
const UserContext = createContext();

function App() {
  const [user, setUser] = useState(null);
  return (
    <UserContext.Provider value={{ user, setUser }}>
      <ChildComponent />
    </UserContext.Provider>
  );
}

Automated Refactoring Support

Safe Refactoring Tools

Use TypeScript or Flow for type-safe code modifications.

interface Props {
  id: number;
  name: string;
}

function Component(props: Props) {
  // The editor provides accurate autocompletion and refactoring support
  return <div>{props.name}</div>;
}

IDE Refactoring Features

Leverage modern IDE features like renaming and function extraction.

// Before extracting function
function process(data) {
  const result = data.map(item => {
    return {
      ...item,
      fullName: `${item.firstName} ${item.lastName}`
    };
  });
}

// After extracting function
function enrichWithFullName(item) {
  return {
    ...item,
    fullName: `${item.firstName} ${item.lastName}`
  };
}

function process(data) {
  const result = data.map(enrichWithFullName);
}

Team Collaboration Standards

Unified Code Style

Use Prettier for automatic code formatting.

// .prettierrc
{
  "semi": false,
  "singleQuote": true,
  "printWidth": 80
}

Git Commit Standards

Conventional Commits improve commit message readability.

feat: Add user login feature
fix: Fix form validation error
docs: Update API documentation
chore: Update dependency versions

Technical Debt Management

Debt Identification

Regularly conduct code reviews to identify technical debt.

// TODO comments mark technical debt
// TODO: Optimize this algorithm; current time complexity is O(n^2)
function slowAlgorithm(data) {
  // ...
}

Debt Tracking

Use issue tracking systems to manage technical debt.

### Issue Description
User list rendering performance significantly degrades when data exceeds 1000 items.

### Suggested Solutions
1. Implement virtual scrolling
2. Load data in pages

### Priority
High