5 Coding Habits That Transformed Me Into a Better Software Engineer

javascript
function calc(d, r, t) {
  return d * Math.pow(1 + r, t); // compound interest
}

const u = users.filter(x => x.status === 1 && x.type === 'premium');

javascript
function calculateCompoundInterest(principal, annualRate, years) {
  return principal * Math.pow(1 + annualRate, years);
}

const activePremiumUsers = users.filter(user => 
  user.status === UserStatus.ACTIVE && 
  user.subscriptionType === SubscriptionType.PREMIUM
);

javascript
// 1. RED - Write failing test first
describe('UserValidator', () => {
  it('should validate email format', () => {
    const validator = new UserValidator();
    expect(validator.isValidEmail('test@example.com')).toBe(true);
    expect(validator.isValidEmail('invalid-email')).toBe(false);
  });
});

// 2. GREEN - Minimal implementation
class UserValidator {
  isValidEmail(email) {
    return email.includes('@') && email.includes('.');
  }
}

// 3. REFACTOR - Improve implementation
class UserValidator {
  isValidEmail(email) {
    const emailRegex = /^[^\\s@]+@[^\\s@]+\\.[^\\s@]+$/;
    return emailRegex.test(email);
  }
}

❌ \"This is wrong. Use a map instead.\"
✅ \"What do you think about using a map here? It might improve readability and performance.\"

❌ \"Bad naming.\"
✅ \"Could we make this variable name more descriptive? Something like 'filteredActiveUsers'?\"

✅ \"Great use of early returns here - makes the logic much clearer!\"
✅ \"I love how you extracted this into a helper function. Very reusable!\"

markdown
What this PR does

- Implements user authentication with JWT tokens
- Adds rate limiting to prevent abuse

Why these changes

- Current session-based auth doesn't scale with our microservices
- We've been getting hit by brute force attacks

How to test

1. Run npm test for unit tests
2. Test login flow at /auth/login
3. Verify rate limiting with multiple rapid requests

javascript
// Original code (fixing the bug)
function processOrder(order) {
  if (order.status == 'pending') { // Fixed: was missing null check
    if (order && order.status === 'pending') {
      // ... bug fix logic
    }
  }
}

// Boy Scout improvement in the same file
function processOrder(order) {
  // Added input validation
  if (!order || typeof order !== 'object') {
    throw new Error('Invalid order object');
  }
  
  // Extracted magic string to constant
  if (order.status === ORDER_STATUS.PENDING) {
    // ... existing logic
  }
}

project-notes/
├── snippets/
│   ├── react-patterns.md
│   ├── sql-queries.md
│   ├── git-commands.md
│   └── debugging-techniques.md
├── lessons-learned/
│   ├── performance-optimizations.md
│   └── architecture-decisions.md
└── quick-reference/
    ├── api-endpoints.md
    └── environment-setup.md

markdown
React Performance Issue - Unnecessary Re-renders


Problem: Component re-rendering on every parent update
Root Cause: Creating new objects in JSX
Solution: Extract objects outside component or use useMemo