---
name: coding-standards
description: Universal coding standards, best practices, and patterns for TypeScript, JavaScript and Node.js development.
version: 1.0.0
license: MIT
authors: [玄子]
---

# Coding Standards & Best Practices

Universal coding standards applicable across all projects.

## When to Activate

- Starting a new project or module
- Reviewing code for quality and maintainability
- Refactoring existing code to follow conventions
- Enforcing naming, formatting, or structural consistency
- Setting up linting, formatting, or type-checking rules
- Onboarding new contributors to coding conventions

## Code Quality Principles

### 1. Readability First
- Code is read more than written
- Clear variable and function names
- Self-documenting code preferred over comments
- Consistent formatting

### 2. KISS (Keep It Simple, Stupid)
- Simplest solution that works
- Avoid over-engineering
- No premature optimization
- Easy to understand > clever code

### 3. DRY (Don't Repeat Yourself)
- Extract common logic into functions
- Create reusable components
- Share utilities across modules
- Avoid copy-paste programming

### 4. YAGNI (You Aren't Gonna Need It)
- Don't build features before they're needed
- Avoid speculative generality
- Add complexity only when required
- Start simple, refactor when needed

## TypeScript/JavaScript Standards

### Variable Naming

```typescript
// ✅ GOOD: Descriptive names
const marketSearchQuery = 'election'
const isUserAuthenticated = true
const totalRevenue = 1000

// ❌ BAD: Unclear names
const q = 'election'
const flag = true
const x = 1000
```

### Function Naming

```typescript
// ✅ GOOD: Verb-noun pattern
async function fetchMarketData(marketId: string) { }
function calculateSimilarity(a: number[], b: number[]) { }
function isValidEmail(email: string): boolean { }

// ❌ BAD: Unclear or noun-only
async function market(id: string) { }
function similarity(a, b) { }
function email(e) { }
```

### Immutability Pattern (CRITICAL)

```typescript
// ✅ ALWAYS use spread operator
const updatedUser = {
  ...user,
  name: 'New Name'
}

const updatedArray = [...items, newItem]

// ❌ NEVER mutate directly
user.name = 'New Name'  // BAD
items.push(newItem)     // BAD
```

### Error Handling

```typescript
// ✅ GOOD: Comprehensive error handling
async function fetchData(url: string) {
  try {
    const response = await fetch(url)

    if (!response.ok) {
      throw new Error(`HTTP ${response.status}: ${response.statusText}`)
    }

    return await response.json()
  } catch (error) {
    console.error('Fetch failed:', error)
    throw new Error('Failed to fetch data')
  }
}

// ❌ BAD: No error handling
async function fetchData(url) {
  const response = await fetch(url)
  return response.json()
}
```

### Async/Await Best Practices

```typescript
// ✅ GOOD: Parallel execution when possible
const [users, markets, stats] = await Promise.all([
  fetchUsers(),
  fetchMarkets(),
  fetchStats()
])

// ❌ BAD: Sequential when unnecessary
const users = await fetchUsers()
const markets = await fetchMarkets()
const stats = await fetchStats()
```

### Type Safety

```typescript
// ✅ GOOD: Proper types
interface Market {
  id: string
  name: string
  status: 'active' | 'resolved' | 'closed'
  created_at: Date
}

function getMarket(id: string): Promise<Market> {
  // Implementation
}

// ❌ BAD: Using 'any'
function getMarket(id: any): Promise<any> {
  // Implementation
}
```


## File Organization

### File Naming

```
components/Button.tsx          # PascalCase for components
hooks/useAuth.ts              # camelCase with 'use' prefix
lib/formatDate.ts             # camelCase for utilities
types/market.types.ts         # camelCase with .types suffix
```

## Comments & Documentation

### When to Comment

```typescript
// ✅ GOOD: Explain WHY, not WHAT
// Use exponential backoff to avoid overwhelming the API during outages
const delay = Math.min(1000 * Math.pow(2, retryCount), 30000)

// Deliberately using mutation here for performance with large arrays
items.push(newItem)

// ❌ BAD: Stating the obvious
// Increment counter by 1
count++

// Set name to user's name
name = user.name
```

### JSDoc for Public APIs

```typescript
/**
 * Searches markets using semantic similarity.
 *
 * @param query - Natural language search query
 * @param limit - Maximum number of results (default: 10)
 * @returns Array of markets sorted by similarity score
 * @throws {Error} If OpenAI API fails or Redis unavailable
 *
 * @example
 * ```typescript
 * const results = await searchMarkets('election', 5)
 * console.log(results[0].name) // "Trump vs Biden"
 * ```
 */
export async function searchMarkets(
  query: string,
  limit: number = 10
): Promise<Market[]> {
  // Implementation
}
```


## Testing Standards

### Test Structure (AAA Pattern)

```typescript
test('calculates similarity correctly', () => {
  // Arrange
  const vector1 = [1, 0, 0]
  const vector2 = [0, 1, 0]

  // Act
  const similarity = calculateCosineSimilarity(vector1, vector2)

  // Assert
  expect(similarity).toBe(0)
})
```

### Test Naming

```typescript
// ✅ GOOD: Descriptive test names
test('returns empty array when no markets match query', () => { })
test('throws error when OpenAI API key is missing', () => { })
test('falls back to substring search when Redis unavailable', () => { })

// ❌ BAD: Vague test names
test('works', () => { })
test('test search', () => { })
```

## Code Smell Detection

Watch for these anti-patterns:

### 1. Long Functions
```typescript
// ❌ BAD: Function > 50 lines
function processMarketData() {
  // 100 lines of code
}

// ✅ GOOD: Split into smaller functions
function processMarketData() {
  const validated = validateData()
  const transformed = transformData(validated)
  return saveData(transformed)
}
```

### 2. Deep Nesting
```typescript
// ❌ BAD: 5+ levels of nesting
if (user) {
  if (user.isAdmin) {
    if (market) {
      if (market.isActive) {
        if (hasPermission) {
          // Do something
        }
      }
    }
  }
}

// ✅ GOOD: Early returns
if (!user) return
if (!user.isAdmin) return
if (!market) return
if (!market.isActive) return
if (!hasPermission) return

// Do something
```

### 3. Magic Numbers
```typescript
// ❌ BAD: Unexplained numbers
if (retryCount > 3) { }
setTimeout(callback, 500)

// ✅ GOOD: Named constants
const MAX_RETRIES = 3
const DEBOUNCE_DELAY_MS = 500

if (retryCount > MAX_RETRIES) { }
setTimeout(callback, DEBOUNCE_DELAY_MS)
```

**Remember**: Code quality is not negotiable. Clear, maintainable code enables rapid development and confident refactoring.