Advanced AI Features: Power User Practice

// Old callback-based API
const fs = require('fs');
const http = require('http');

function getUserData(id, callback) {
  fs.readFile(`users/${id}.json`, (err, data) => {
    if (err) callback(err, null);
    else callback(null, JSON.parse(data));
  });
}

function updateUser(id, data, callback) {
  fs.writeFile(`users/${id}.json`, JSON.stringify(data), callback);
}

// jQuery-based frontend
$(document).ready(function() {
  $('#load-user').click(function() {
    var userId = $('#user-id').val();
    $.get('/api/user/' + userId, function(data) {
      $('#user-name').text(data.name);
      $('#user-email').text(data.email);
    });
  });
});

Refactor this entire legacy codebase to modern standards:

BACKEND CHANGES:
- Convert to async/await from callbacks
- Use Express.js instead of raw HTTP
- Add proper error handling and validation
- Implement RESTful endpoints
- Add TypeScript types
- Include request/response logging

FRONTEND CHANGES:
- Convert from jQuery to modern vanilla JavaScript
- Use fetch API instead of jQuery AJAX  
- Add loading states and error handling
- Implement modern ES6+ features
- Make it responsive and accessible

ARCHITECTURE:
- Separate concerns (routes, controllers, services)
- Add configuration management
- Include database connection setup
- Add middleware for common functionality

QUALITY:
- Add comprehensive error handling
- Include input validation
- Add security headers
- Implement rate limiting
- Add unit tests for core functions

// memory-leak.js
let cache = new Map();

function processData(data) {
  const id = Math.random().toString(36);
  const processor = {
    data: data,
    process: function() {
      // Simulate heavy processing
      let result = JSON.parse(JSON.stringify(data));
      cache.set(id, result);
      return result;
    }
  };
  
  setInterval(() => {
    cache.set(Math.random().toString(), data);
  }, 100);
  
  return processor.process();
}

// This will cause memory issues
for(let i = 0; i < 1000; i++) {
  processData({large: new Array(1000).fill('data')});
}

Debug this JavaScript memory leak:

CONTEXT:
- This function processes data and caches results
- Memory usage keeps growing
- Application eventually crashes

ANALYSIS NEEDED:
1. Identify what's causing the memory leak
2. Explain why it's problematic  
3. Provide 3 different solution approaches
4. Implement the best solution
5. Add monitoring to prevent future leaks

REQUIREMENTS:
- Must maintain original functionality
- Add memory usage tracking
- Include cleanup mechanisms
- Add warnings for excessive memory use

// race-condition.js
let counter = 0;
let results = [];

async function fetchData(id) {
  // Simulate API call
  await new Promise(resolve => setTimeout(resolve, Math.random() * 1000));
  return `data-${id}`;
}

async function processData() {
  for(let i = 0; i < 10; i++) {
    fetchData(i).then(data => {
      counter++;
      results[i] = data;
      console.log(`Processed ${counter}/10: ${data}`);
    });
  }
}

processData();

Fix this race condition bug:

PROBLEM:
- Results array has undefined values
- Counter doesn't match expected results
- Output order is unpredictable

SOLUTION REQUIREMENTS:
- Ensure all data is processed
- Maintain order of results
- Provide predictable timing
- Add error handling for failed requests
- Include progress tracking

BONUS:
- Show 3 different approaches (Promise.all, async iteration, queue-based)
- Explain trade-offs of each approach
- Implement the most robust solution

Create a real-time collaborative text editor with these specifications:

CORE FUNCTIONALITY:
- Rich text editing (bold, italic, underline, headings)
- Real-time collaboration (simulate with localStorage for now)
- Document versioning and history
- Auto-save functionality
- Word count and reading time
- Export to PDF and Markdown

ARCHITECTURE REQUIREMENTS:
- Modular component design
- Event-driven architecture
- Conflict resolution for concurrent edits
- Efficient diff algorithm for changes
- Undo/redo system with branching

UI/UX SPECIFICATIONS:
- Modern, clean interface like Notion or Google Docs
- Floating toolbar for formatting
- Sidebar for document outline
- Status bar with word count, save status
- Responsive design for mobile/desktop
- Dark/light theme toggle

TECHNICAL REQUIREMENTS:
- Vanilla JavaScript (no frameworks)
- Progressive Web App capabilities
- Accessibility compliance (ARIA labels, keyboard navigation)
- Performance optimizations for large documents
- Error boundaries and graceful failures

ADVANCED FEATURES:
- Collaborative cursors (show other users' positions)
- Comments and suggestions system
- Document sharing with permissions
- Search and replace with regex support
- Table insertion and editing
- Image upload and embedding

CODE QUALITY:
- TypeScript-style JSDoc comments
- Comprehensive error handling
- Unit tests for critical functions
- Performance monitoring
- Security considerations (XSS prevention)

// slow-dashboard.js
function loadDashboard() {
  // Simulate heavy operations
  const data = [];
  for(let i = 0; i < 10000; i++) {
    data.push({
      id: i,
      name: `User ${i}`,
      email: `user${i}@example.com`,
      metrics: calculateMetrics(i),
      history: generateHistory(i)
    });
  }
  
  renderCharts(data);
  renderTables(data);
  renderMaps(data);
}

function calculateMetrics(id) {
  // Expensive calculation
  let result = 0;
  for(let i = 0; i < 1000000; i++) {
    result += Math.sin(id * i) * Math.cos(id * i);
  }
  return result;
}

function renderCharts(data) {
  // Re-renders everything on each update
  document.getElementById('charts').innerHTML = '';
  data.forEach(item => {
    const chart = document.createElement('div');
    chart.innerHTML = `<canvas id="chart-${item.id}"></canvas>`;
    document.getElementById('charts').appendChild(chart);
    drawChart(item);
  });
}

Optimize this slow dashboard for production performance:

PERFORMANCE ISSUES TO FIX:
1. Expensive calculations blocking UI
2. Unnecessary re-renders
3. Memory leaks from DOM manipulation
4. No caching of computed values
5. Inefficient data structures

OPTIMIZATION TECHNIQUES TO IMPLEMENT:
- Web Workers for heavy calculations
- Virtual scrolling for large lists
- Memoization for expensive operations
- Efficient DOM updates (virtual DOM concepts)
- Lazy loading for off-screen content
- Request batching and debouncing
- Memory management optimizations

PERFORMANCE TARGETS:
- Initial load: < 2 seconds
- Interactions: < 100ms response
- Memory usage: < 50MB
- 60fps smooth scrolling
- Works on mobile devices

MONITORING:
- Add performance metrics collection
- Implement real-user monitoring
- Create performance budgets
- Add automated performance tests

Design and implement a microservices communication pattern:

SERVICES TO CREATE:
1. User Service - handles authentication/profiles
2. Order Service - manages purchase orders  
3. Inventory Service - tracks product stock
4. Notification Service - sends emails/SMS
5. API Gateway - routes and aggregates requests

COMMUNICATION PATTERNS:
- Synchronous: HTTP REST APIs with retries
- Asynchronous: Event-driven messaging
- Circuit breaker pattern for fault tolerance
- Saga pattern for distributed transactions
- CQRS for read/write separation

TECHNICAL IMPLEMENTATION:
- Each service as separate Node.js application
- Redis for event streaming
- JSON Web Tokens for authentication
- Request/response correlation IDs
- Comprehensive logging and monitoring

RESILIENCE PATTERNS:
- Health checks for all services
- Graceful degradation
- Timeout and retry mechanisms
- Bulkhead pattern for resource isolation
- Load balancing strategies

TESTING STRATEGY:
- Unit tests for business logic
- Contract tests between services
- Integration tests for workflows
- Chaos engineering scenarios
- Performance testing under load

// problematic-code.js
var userData = {};
function login(user, pass) {
  if(user == "admin" && pass == "password123") {
    userData = {name: user, role: "admin"};
    localStorage.setItem("user", JSON.stringify(userData));
    return true;
  }
  return false;
}

function deleteUser(id) {
  fetch("/api/users/" + id, {method: "DELETE"})
    .then(res => res.json())
    .then(data => alert("User deleted!"))
    .catch(err => console.log(err));
}

$(document).ready(function(){
  $(".delete-btn").click(function(){
    deleteUser($(this).data("id"));
  });
});

Perform a comprehensive security and quality review of this code:

SECURITY ANALYSIS:
- Identify all security vulnerabilities
- Rate severity (Critical/High/Medium/Low)
- Provide specific exploit scenarios
- Recommend security fixes

CODE QUALITY REVIEW:
- Modern JavaScript best practices
- Error handling improvements
- Performance considerations
- Accessibility issues
- Maintainability concerns

ARCHITECTURAL IMPROVEMENTS:
- Suggest better patterns
- Recommend refactoring approach
- Consider scalability issues
- Address technical debt

PROVIDE:
1. Line-by-line issue analysis
2. Priority-ranked fix recommendations
3. Refactored code implementation
4. Prevention strategies for similar issues