Coding Standards

Coding Standards & Best Practices

Baseline coding conventions applicable across projects.

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

• Use frontend-patterns for React, state, forms, rendering, and UI architecture.
• Use backend-patterns or api-design for repository/service layers, endpoint design, validation, and server-specific concerns.
• 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

// 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

// 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)

// 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

// 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

// 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

// PASS: GOOD: Proper types
interface 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

// PASS: GOOD: Functional component with types
interface ButtonProps {
  children: React.ReactNode
  onClick: () => void
  disabled?: boolean
  variant?: 'primary' | 'secondary'
}

export function Button({
  children,
  onClick,
  disabled = false,
  variant = 'primary'
}: ButtonProps) {
  return (
    <button
      onClick={onClick}
      disabled={disabled}
      className={`btn btn-${variant}`}
    >
      {children}
    </button>
  )
}

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

Custom Hooks

// 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

// 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

// 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

// PASS: GOOD: Consistent response structure
interface 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

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.errors
      }, { status: 400 })
    }
  }
}

File Organization

Project Structure

src/
├── app/                    # Next.js App Router
│   ├── api/               # API routes
│   ├── markets/           # Market pages
│   └── (auth)/           # Auth pages (route groups)
├── components/            # React components
│   ├── ui/               # Generic UI components
│   ├── forms/            # Form components
│   └── layouts/          # Layout components
├── hooks/                # Custom React hooks