JavaScript: Modern Data Handling Techniques Guide

// Modern array transformation pipeline
const processUserData = (users) => {
  return users
    .filter(user => user.active)
    .map(user => ({
      ...user,
      fullName: `${user.firstName} ${user.lastName}`,
      membershipYears: new Date().getFullYear() - user.joinYear
    }))
    .sort((a, b) => b.membershipYears - a.membershipYears)
    .slice(0, 10);
};

// Destructuring and spread operations
const [first, second, ...remaining] = processedUsers;
const updatedUsers = [...activeUsers, ...newUsers];

// Modern class with data handling methods
class DataProcessor {
  constructor(config = {}) {
    this.config = { ...this.defaultConfig, ...config };
    this.cache = new Map();
  }

  // Method with destructuring and default parameters
  processItem({ id, data, metadata = {} }) {
    const { transform, validate } = this.config;
    
    if (validate && !this.isValid(data)) {
      throw new Error(`Invalid data for item ${id}`);
    }

    const processed = transform ? transform(data) : data;
    const result = { id, processed, metadata, timestamp: Date.now() };
    
    this.cache.set(id, result);
    return result;
  }

  // Async data processing with error handling
  async batchProcess(items) {
    const results = await Promise.allSettled(
      items.map(item => this.processItem(item))
    );

    return results.map((result, index) => ({
      index,
      success: result.status === 'fulfilled',
      data: result.status === 'fulfilled' ? result.value : null,
      error: result.status === 'rejected' ? result.reason : null
    }));
  }
}

// Functional composition for data transformation
const pipe = (...functions) => (value) => 
  functions.reduce((acc, func) => func(acc), value);

const transformData = pipe(
  data => data.filter(item => item.active),
  data => data.map(item => normalizeItem(item)),
  data => data.sort((a, b) => a.priority - b.priority),
  data => groupBy(data, 'category')
);

// Async transformation pipeline
const processAsync = async (data) => {
  const validated = await validateData(data);
  const transformed = await Promise.all(
    validated.map(async item => {
      const enriched = await enrichWithExternalData(item);
      return transform(enriched);
    })
  );
  return aggregateResults(transformed);
};

// Comprehensive validation with error handling
class DataValidator {
  static validateUser(userData) {
    const errors = [];
    
    if (!userData || typeof userData !== 'object') {
      throw new Error('Invalid user data: must be an object');
    }

    // Required field validation
    const required = ['email', 'name'];
    required.forEach(field => {
      if (!userData[field] || typeof userData[field] !== 'string') {
        errors.push(`${field} is required and must be a string`);
      }
    });

    // Email format validation
    if (userData.email && !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(userData.email)) {
      errors.push('Invalid email format');
    }

    // Age validation if provided
    if (userData.age !== undefined) {
      if (!Number.isInteger(userData.age) || userData.age < 0 || userData.age > 150) {
        errors.push('Age must be a valid integer between 0 and 150');
      }
    }

    if (errors.length > 0) {
      throw new ValidationError('User validation failed', errors);
    }

    return true;
  }
}

// Custom error class for better error handling
class ValidationError extends Error {
  constructor(message, validationErrors) {
    super(message);
    this.name = 'ValidationError';
    this.validationErrors = validationErrors;
  }
}

// Advanced async data processing patterns
class AsyncDataProcessor {
  // Parallel processing with concurrency limits
  async processInBatches(items, batchSize = 5) {
    const results = [];
    
    for (let i = 0; i < items.length; i += batchSize) {
      const batch = items.slice(i, i + batchSize);
      const batchResults = await Promise.allSettled(
        batch.map(item => this.processItem(item))
      );
      results.push(...batchResults);
    }
    
    return results;
  }

  // Retry mechanism with exponential backoff
  async processWithRetry(item, maxRetries = 3) {
    for (let attempt = 1; attempt <= maxRetries; attempt++) {
      try {
        return await this.processItem(item);
      } catch (error) {
        if (attempt === maxRetries) throw error;
        
        const delay = Math.pow(2, attempt) * 1000; // Exponential backoff
        await new Promise(resolve => setTimeout(resolve, delay));
      }
    }
  }

  // Stream processing with async generators
  async* processStream(dataStream) {
    for await (const chunk of dataStream) {
      try {
        const processed = await this.transformChunk(chunk);
        yield processed;
      } catch (error) {
        console.error('Chunk processing failed:', error);
        yield { error: error.message, chunk };
      }
    }
  }
}