frontend-dev-guidelines

# Frontend Development Guidelines

## Purpose

Comprehensive guide for modern React development, emphasizing Suspense-based data fetching, lazy loading, proper file organization, and performance optimization.

## When to Use This Skill

- Creating new components or pages
- Building new features
- Fetching data with TanStack Query
- Setting up routing with TanStack Router
- Styling components with MUI v7
- Performance optimization
- Organizing frontend code
- TypeScript best practices

---

## Quick Start

### New Component Checklist

Creating a component? Follow this checklist:

- [ ] Use `React.FC<Props>` pattern with TypeScript
- [ ] Lazy load if heavy component: `React.lazy(() => import())`
- [ ] Wrap in `<SuspenseLoader>` for loading states
- [ ] Use `useSuspenseQuery` for data fetching
- [ ] Import aliases: `@/`, `~types`, `~components`, `~features`
- [ ] Styles: Inline if <100 lines, separate file if >100 lines
- [ ] Use `useCallback` for event handlers passed to children
- [ ] Default export at bottom
- [ ] No early returns with loading spinners
- [ ] Use `useMuiSnackbar` for user notifications

### New Feature Checklist

Creating a feature? Set up this structure:

- [ ] Create `features/{feature-name}/` directory
- [ ] Create subdirectories: `api/`, `components/`, `hooks/`, `helpers/`, `types/`
- [ ] Create API service file: `api/{feature}Api.ts`
- [ ] Set up TypeScript types in `types/`
- [ ] Create route in `routes/{feature-name}/index.tsx`
- [ ] Lazy load feature components
- [ ] Use Suspense boundaries
- [ ] Export public API from feature `index.ts`

---

## Import Aliases Quick Reference

| Alias | Resolves To | Example |
|-------|-------------|---------|
| `@/` | `src/` | `import { apiClient } from '@/lib/apiClient'` |
| `~types` | `src/types` | `import type { User } from '~types/user'` |
| `~components` | `src/components` | `import { SuspenseLoader } from '~components/SuspenseLoader'` |
| `~features` | `src/features` | `import { authApi } from '~features/auth'` |

Defined in: [vite.config.ts](../../vite.config.ts) lines 180-185

---

## Common Imports Cheatsheet

```typescript
// React & Lazy Loading
import React, { useState, useCallback, useMemo } from 'react';
const Heavy = React.lazy(() => import('./Heavy'));

// MUI Components
import { Box, Paper, Typography, Button, Grid } from '@mui/material';
import type { SxProps, Theme } from '@mui/material';

// TanStack Query (Suspense)
import { useSuspenseQuery, useQueryClient } from '@tanstack/react-query';

// TanStack Router
import { createFileRoute } from '@tanstack/react-router';

// Project Components
import { SuspenseLoader } from '~components/SuspenseLoader';

// Hooks
import { useAuth } from '@/hooks/useAuth';
import { useMuiSnackbar } from '@/hooks/useMuiSnackbar';

// Types
import type { Post } from '~types/post';
```

---

## Topic Guides

### 🎨 Component Patterns

**Modern React components use:**
- `React.FC<Props>` for type safety
- `React.lazy()` for code splitting
- `SuspenseLoader` for loading states
- Named const + default export pattern

**Key Concepts:**
- Lazy load heavy components (DataGrid, charts, editors)
- Always wrap lazy components in Suspense
- Use SuspenseLoader component (with fade animation)
- Component structure: Props → Hooks → Handlers → Render → Export

**[📖 Complete Guide: resources/component-patterns.md](resources/component-patterns.md)**

---

### 📊 Data Fetching

**PRIMARY PATTERN: useSuspenseQuery**
- Use with Suspense boundaries
- Cache-first strategy (check grid cache before API)
- Replaces `isLoading` checks
- Type-safe with generics

**API Service Layer:**
- Create `features/{feature}/api/{feature}Api.ts`
- Use `apiClient` axios instance
- Centralized methods per feature
- Route format: `/form/route` (NOT `/api/form/route`)

**[📖 Complete Guide: resources/data-fetching.md](resources/data-fetching.md)**

---

### 📁 File Organization

**features/ vs components/:**
- `features/`: Domain-specific (posts, comments, auth)
- `components/`: Truly reusable (SuspenseLoader, CustomAppBar)

**Feature Subdirectories:**
```
features/
  my-feature/
    api/          # API service layer
    components/   # Feature components
    hooks/        # Custom hooks
    helpers/      # Utility functions
    types/        # TypeScript types
```

**[📖 Complete Guide: resources/file-organization.md](resources/file-organization.md)**

---

### 🎨 Styling

**Inline vs Separate:**
- <100 lines: Inline `const styles: Record<string, SxProps<Theme>>`
- >100 lines: Separate `.styles.ts` file

**Primary Method:**
- Use `sx` prop for MUI components
- Type-safe with `SxProps<Theme>`
- Theme access: `(theme) => theme.palette.primary.main`

**MUI v7 Grid:**
```typescript
<Grid size={{ xs: 12, md: 6 }}>  // ✅ v7 syntax
<Grid xs={12} md={6}>             // ❌ Old syntax
```

**[📖 Complete Guide: resources/styling-guide.md](resources/styling-guide.md)**

---

### 🛣️ Routing

**TanStack Router - Folder-Based:**
- Directory: `routes/my-route/index.tsx`
- Lazy load components
- Use `createFileRoute`
- Breadcrumb data in loader

**Example:**
```typescript
import { createFileRoute } from '@tanstack/react-router';
import { lazy } from 'react';

const MyPage = lazy(() => import('@/features/my-feature/components/MyPage'));

export const Route = createFileRoute('/my-route/')({
    component: MyPage,
    loader: () => ({ crumb: 'My Route' }),
});
```

**[📖 Complete Guide: resources/routing-guide.md](resources/routing-guide.md)**

---

### ⏳ Loading & Error States

**CRITICAL RULE: No Early Returns**

```typescript
// ❌ NEVER - Causes layout shift
if (isLoading) {
    return <LoadingSpinner />;
}

// ✅ ALWAYS - Consistent layout
<SuspenseLoader>
    <Content />
</SuspenseLoader>
```

**Why:** Prevents Cumulative Layout Shift (CLS), better UX

**Error Handling:**
- Use `useMuiSnackbar` for user feedback
- NEVER `react-toastify`
- TanStack Query `onError` callbacks

**[📖 Complete Guide: resources/loading-and-error-states.md](res