Identification and Implementation Steps of Pattern Refactoring

Pattern Refactoring: Identification and Implementation Steps

Refactoring is a crucial means of improving code quality, especially in JavaScript design pattern applications. Identifying patterns that need refactoring and correctly implementing the steps is essential. Pattern refactoring not only optimizes existing code structures but also makes the application of design patterns more efficient and flexible.

Identifying Patterns That Need Refactoring

Code Duplication and Redundancy

Duplicate code is the primary signal for refactoring. When similar logic appears in multiple places, it may indicate the need to introduce a design pattern. For example, multiple components may have similar form validation logic:

// Duplicate validation logic
function validateEmail(email) {
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);
}

function validatePassword(password) {
  return password.length >= 8;
}

// After refactoring, extract as a strategy pattern
const validationStrategies = {
  email: (value) => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(value),
  password: (value) => value.length >= 8
};

Complex Conditional Statements

When encountering complex conditional branches, especially those based on types, it may be suitable to refactor using the Factory Pattern or Strategy Pattern:

// Complex conditions before refactoring
function createAnimal(type) {
  if (type === 'dog') {
    return new Dog();
  } else if (type === 'cat') {
    return new Cat();
  }
  throw new Error('Invalid animal type');
}

// Refactored as Factory Pattern
class AnimalFactory {
  static create(type) {
    const creators = {
      dog: () => new Dog(),
      cat: () => new Cat()
    };
    return creators[type]?.() ?? throw new Error('Invalid animal type');
  }
}

Chaotic Global State Management

When shared state between components becomes difficult to maintain, consider introducing the Observer Pattern or Singleton Pattern:

// Chaotic global state
let globalCounter = 0;

// Refactored as Observer Pattern
class Counter {
  constructor() {
    this.value = 0;
    this.observers = [];
  }
  
  subscribe(observer) {
    this.observers.push(observer);
  }
  
  increment() {
    this.value++;
    this.notify();
  }
  
  notify() {
    this.observers.forEach(obs => obs.update(this.value));
  }
}

Refactoring Implementation Steps

1. Establish Test Coverage

Ensure sufficient test coverage before starting refactoring:

// Write tests using Jest
describe('Counter', () => {
  let counter;
  
  beforeEach(() => {
    counter = new Counter();
  });
  
  test('increment increases value', () => {
    counter.increment();
    expect(counter.value).toBe(1);
  });
});

2. Small Incremental Refactoring

Adopt a step-by-step approach, making only small changes at a time:

// Original code
function processData(data) {
  // Complex processing logic
  const result1 = step1(data);
  const result2 = step2(result1);
  return step3(result2);
}

// First refactoring step: Extract methods
function processData(data) {
  const result1 = processStep1(data);
  const result2 = processStep2(result1);
  return processStep3(result2);
}

3. Apply Design Patterns

Choose the appropriate pattern based on identified issues:

// Apply Decorator Pattern
class BasicLogger {
  log(message) {
    console.log(message);
  }
}

class TimestampLoggerDecorator {
  constructor(logger) {
    this.logger = logger;
  }
  
  log(message) {
    this.logger.log(`[${new Date().toISOString()}] ${message}`);
  }
}

const logger = new TimestampLoggerDecorator(new BasicLogger());

4. Verify and Iterate

Run tests and check functionality after refactoring:

// Verify Decorator Pattern
logger.log('Test message'); // Outputs timestamped log

Common Refactoring Scenarios and Pattern Selection

Chaotic Event Handling → Observer Pattern

When there are too many event listeners and they become difficult to manage:

// Before refactoring
document.addEventListener('click', handler1);
document.addEventListener('click', handler2);

// Refactored as Event Bus
class EventBus {
  constructor() {
    this.events = {};
  }
  
  on(event, callback) {
    this.events[event] = this.events[event] || [];
    this.events[event].push(callback);
  }
  
  emit(event, ...args) {
    this.events[event]?.forEach(cb => cb(...args));
  }
}

Complex Component Configuration → Builder Pattern

When object construction requires multiple steps:

// Before refactoring
const widget = new Widget({
  title: 'My Widget',
  size: 'large',
  theme: 'dark'
});

// Refactored as Builder Pattern
class WidgetBuilder {
  constructor() {
    this.widget = new Widget();
  }
  
  setTitle(title) {
    this.widget.title = title;
    return this;
  }
  
  setSize(size) {
    this.widget.size = size;
    return this;
  }
  
  build() {
    return this.widget;
  }
}

const widget = new WidgetBuilder()
  .setTitle('My Widget')
  .setSize('large')
  .build();

Maintaining Refactored Code

Documenting Pattern Applications

Add comments to explain design patterns in refactored code:

/**
 * Implements validation logic using Strategy Pattern
 * Allows dynamic addition of new validation strategies without modifying existing code
 */
class Validator {
  constructor() {
    this.strategies = {};
  }
  
  addStrategy(name, strategy) {
    this.strategies[name] = strategy;
  }
  
  validate(name, value) {
    return this.strategies[name]?.(value) ?? false;
  }
}

Performance Considerations

Some design patterns may impact performance and require trade-offs:

// Performance considerations for Proxy Pattern
class ExpensiveOperationProxy {
  constructor() {
    this.cache = new Map();
  }
  
  compute(key) {
    if (this.cache.has(key)) {
      return this.cache.get(key);
    }
    const result = expensiveComputation(key);
    this.cache.set(key, result);
    return result;
  }
}

Refactoring Practices in Team Collaboration

Code Review Focus Points

During code reviews, pay special attention to:

1. Whether the pattern application is appropriate
2. Whether original functionality is preserved
3. Whether there are better pattern choices

Refactoring Records

Maintain complete refactoring records:

## Refactoring Log

2023-05-01: 
- Changed form validation to Strategy Pattern
- Motivation: Eliminate duplicate validation logic
- Affected files: validation.js, form-components/

Refactoring Tools and Techniques

Static Analysis Tools

Use tools like ESLint to identify refactoring opportunities:

{
  "rules": {
    "max-depth": ["error", 4],
    "complexity": ["error", 5]
  }
}

IDE Refactoring Features

Utilize modern IDE refactoring features:

1. Extract method
2. Rename symbol
3. Inline variable

Advanced Techniques for Pattern Refactoring

Pattern Composition

Combine multiple design patterns to solve complex problems:

// Combining Factory Method and Singleton patterns
class LoggerFactory {
  static getInstance(type) {
    if (!this.instances) {
      this.instances = {};
    }
    
    if (!this.instances[type]) {
      this.instances[type] = this.createLogger(type);
    }
    
    return this.instances[type];
  }
  
  static createLogger(type) {
    switch(type) {
      case 'file': return new FileLogger();
      case 'console': return new ConsoleLogger();
    }
  }
}

Parameterizing Patterns

Make patterns more flexible:

// Configurable Observer Pattern
class Observable {
  constructor(options = {}) {
    this.observers = [];
    this.async = options.async || false;
  }
  
  notify(data) {
    const notifyObserver = (observer) => {
      try {
        observer.update(data);
      } catch (err) {
        console.error('Observer error:', err);
      }
    };
    
    if (this.async) {
      this.observers.forEach(obs => setTimeout(() => notifyObserver(obs), 0));
    } else {
      this.observers.forEach(notifyObserver);
    }
  }
}