coding-standards

---
name: coding-standards
description: Baseline cross-project coding conventions for naming, readability, immutability, and code-quality review. Use detailed frontend or backend skills for framework-specific patterns. Use when reviewing code quality or naming with no framework-specific skill that applies.
metadata:
  origin: ECC
---

# Coding Standards & Best Practices

Baseline coding conventions applicable across projects.

This skill is the shared floor, not the detailed framework playbook.

- Use `react-patterns` for React, state, forms, rendering, and UI architecture.
- Use `node-patterns` or `api-design` for repository/service layers, endpoint design, validation, and server-specific concerns.
- Use `rust-patterns` for any Rust code.
- Use `rules/common/coding-style.md` when you need the shortest reusable rule layer instead of a full skill walkthrough.

## 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

## Scope Boundaries

Activate this skill for:
- descriptive naming
- immutability defaults
- readability, KISS, DRY, and YAGNI enforcement
- error-handling expectations and code-smell review

Do not use this skill as the primary source for:
- React composition, hooks, or rendering patterns
- backend architecture, API design, or database layering
- domain-specific framework guidance when a narrower ECC skill already exists

## 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
// PASS: GOOD: Descriptive names
const marketSearchQuery = 'election'
const isUserAuthenticated = true
const totalRevenue = 1000

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

### Function Naming

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

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

### Immutability Pattern (CRITICAL)

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

const updatedArray = [...items, newItem]

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

### Error Handling

```typescript
// PASS: 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')
  }
}

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

### Async/Await Best Practices

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

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

### Type Safety

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

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

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

## React Best Practices

### Component Structure

```typescript
// PASS: GOOD: Functional component with types, named return type, no destructuring
type ButtonProps = {
  children: React.ReactNode
  onClick: () => void
  disabled?: boolean
  variant?: 'primary' | 'secondary'
}
type ButtonReturnType = JSX.Element

export function Button(props: ButtonProps): ButtonReturnType {
  const disabled = props.disabled ?? false
  const variant = props.variant ?? 'primary'

  return (
    <button
      onClick={props.onClick}
      disabled={disabled}
      className={`btn btn-${variant}`}
    >
      {props.children}
    </button>
  )
}

// FAIL: BAD: No types, unclear structure
export function Button(props) {
  return <button onClick={props.onClick}>{props.children}</button>
}
```

### Custom Hooks

```typescript
// PASS: GOOD: Reusable custom hook
export function useDebounce<T>(value: T, delay: number): T {
  const [debouncedValue, setDebouncedValue] = useState<T>(value)

  useEffect(() => {
    const handler = setTimeout(() => {
      setDebouncedValue(value)
    }, delay)

    return () => clearTimeout(handler)
  }, [value, delay])

  return debouncedValue
}

// Usage
const debouncedQuery = useDebounce(searchQuery, 500)
```

### State Management

```typescript
// PASS: GOOD: Proper state updates
const [count, setCount] = useState(0)

// Functional update for state based on previous state
setCount(prev => prev + 1)

// FAIL: BAD: Direct state reference
setCount(count + 1)  // Can be stale in async scenarios
```

### Conditional Rendering

```typescript
// PASS: GOOD: Clear conditional rendering
{isLoading && <Spinner />}
{error && <ErrorMessage error={error} />}
{data && <DataDisplay data={data} />}

// FAIL: BAD: Ternary hell
{isLoading ? <Spinner /> : error ? <ErrorMessage error={error} /> : data ? <DataDisplay data={data} /> : null}
```

## API Design Standards

### REST API Conventions

```
GET    /api/markets              # List all markets
GET    /api/markets/:id          # Get specific market
POST   /api/markets              # Create new market
PUT    /api/markets/:id          # Update market (full)
PATCH  /api/markets/:id          # Update market (partial)
DELETE /api/markets/:id          # Delete market

# Query parameters for filtering
GET /api/markets?status=active&limit=10&offset=0
```

### Response Format

```typescript
// PASS: GOOD: Consistent response structure
type ApiResponse<T> = {
  success: boolean
  data?: T
  error?: string
  meta?: {
    total: number
    page: number
    limit: number
  }
}

// Success response
return NextResponse.json({
  success: true,
  data: markets,
  meta: { total: 100, page: 1, limit: 10 }
})

// Error response
return NextResponse.json({
  success: false,
  error: 'Invalid request'
}, { status: 400 })
```

### Input Validation

```typescript
import { z } from 'zod'

// PASS: GOOD: Schema validation
const CreateMarketSchema = z.object({
  name: z.string().min(1).max(200),
  description: z.string().min(1).max(2000),
  endDate: z.string().datetime(),
  categories: z.array(z.string()).min(1)
})

export async function POST(request: Request) {
  const body = await request.json()

  try {
    const validated = CreateMarketSchema.parse(body)
    // Proceed with validated data
  } catch (error) {
    if (error instanceof z.ZodError) {
      return NextResponse.json({
        success: false,
        error: 'Validation failed',
        details: error.issues
      }, { status: 400 })
    }
  }
}
```


## Further Reference

File organization, comment/documentation conventions, performance best practices, test
structure/naming, and code smell detection are in `references/organization-and-smells.md`.

• SKILL.md 8 KB
• references/organization-and-smells.md 5 KB