senior-frontend v1.0.0A

Immutable. This exact content is served forever at /api/v1/blob/ebc2ad8dab432405.

---
name: senior-frontend
description: >
  Frontend development for React, Next.js, TypeScript, and Tailwind CSS. Use when building
  React components, optimizing Next.js performance, analyzing bundle sizes, scaffolding
  projects, implementing accessibility, or reviewing frontend code.
license: MIT + Commons Clause
metadata:
  version: 1.0.0
  author: borghei
  category: engineering
  domain: frontend
  updated: 2026-03-31
  tags: [react, typescript, accessibility, performance, state-management]
---
# Senior Frontend

Frontend development patterns, performance optimization, and automation tools for React/Next.js applications.

## Table of Contents

- [Project Scaffolding](#project-scaffolding)
- [Component Generation](#component-generation)
- [Bundle Analysis](#bundle-analysis)
- [React Patterns](#react-patterns)
- [Next.js Optimization](#nextjs-optimization)
- [Accessibility and Testing](#accessibility-and-testing)

---

## Project Scaffolding

Generate a new Next.js or React project with TypeScript, Tailwind CSS, and best practice configurations.

### Workflow: Create New Frontend Project

1. Run the scaffolder with your project name and template:
   ```bash
   python scripts/frontend_scaffolder.py my-app --template nextjs
   ```

2. Add optional features (auth, api, forms, testing, storybook):
   ```bash
   python scripts/frontend_scaffolder.py dashboard --template nextjs --features auth,api
   ```

3. Navigate to the project and install dependencies:
   ```bash
   cd my-app && npm install
   ```

4. Start the development server:
   ```bash
   npm run dev
   ```

### Scaffolder Options

| Option | Description |
|--------|-------------|
| `--template nextjs` | Next.js 14+ with App Router and Server Components |
| `--template react` | React + Vite with TypeScript |
| `--features auth` | Add NextAuth.js authentication |
| `--features api` | Add React Query + API client |
| `--features forms` | Add React Hook Form + Zod validation |
| `--features testing` | Add Vitest + Testing Library |
| `--dry-run` | Preview files without creating them |

### Generated Structure (Next.js)

```
my-app/
├── app/
│   ├── layout.tsx        # Root layout with fonts
│   ├── page.tsx          # Home page
│   ├── globals.css       # Tailwind + CSS variables
│   └── api/health/route.ts
├── components/
│   ├── ui/               # Button, Input, Card
│   └── layout/           # Header, Footer, Sidebar
├── hooks/                # useDebounce, useLocalStorage
├── lib/                  # utils (cn), constants
├── types/                # TypeScript interfaces
├── tailwind.config.ts
├── next.config.js
└── package.json
```

---

## Component Generation

Generate React components with TypeScript, tests, and Storybook stories.

### Workflow: Create a New Component

1. Generate a client component:
   ```bash
   python scripts/component_generator.py Button --dir src/components/ui
   ```

2. Generate a server component:
   ```bash
   python scripts/component_generator.py ProductCard --type server
   ```

3. Generate with test and story files:
   ```bash
   python scripts/component_generator.py UserProfile --with-test --with-story
   ```

4. Generate a custom hook:
   ```bash
   python scripts/component_generator.py FormValidation --type hook
   ```

### Generator Options

| Option | Description |
|--------|-------------|
| `--type client` | Client component with 'use client' (default) |
| `--type server` | Async server component |
| `--type hook` | Custom React hook |
| `--with-test` | Include test file |
| `--with-story` | Include Storybook story |
| `--flat` | Create in output dir without subdirectory |
| `--dry-run` | Preview without creating files |

### Generated Component Example

```tsx
'use client';

import { useState } from 'react';
import { cn } from '@/lib/utils';

interface ButtonProps {
  className?: string;
  children?: React.ReactNode;
}

export function Button({ className, children }: ButtonProps) {
  return (
    <div className={cn('', className)}>
      {children}
    </div>
  );
}
```

---

## Bundle Analysis

Analyze package.json and project structure for bundle optimization opportunities.

### Workflow: Optimize Bundle Size

1. Run the analyzer on your project:
   ```bash
   python scripts/bundle_analyzer.py /path/to/project
   ```

2. Review the health score and issues:
   ```
   Bundle Health Score: 75/100 (C)

   HEAVY DEPENDENCIES:
     moment (290KB)
       Alternative: date-fns (12KB) or dayjs (2KB)

     lodash (71KB)
       Alternative: lodash-es with tree-shaking
   ```

3. Apply the recommended fixes by replacing heavy dependencies.

4. Re-run with verbose mode to check import patterns:
   ```bash
   python scripts/bundle_analyzer.py . --verbose
   ```

### Bundle Score Interpretation

| Score | Grade | Action |
|-------|-------|--------|
| 90-100 | A | Bundle is well-optimized |
| 80-89 | B | Minor optimizations available |
| 70-79 | C | Replace heavy dependencies |
| 60-69 | D | Multiple issues need attention |
| 0-59 | F | Critical bundle size problems |

### Heavy Dependencies Detected

The analyzer identifies these common heavy packages:

| Package | Size | Alternative |
|---------|------|-------------|
| moment | 290KB | date-fns (12KB) or dayjs (2KB) |
| lodash | 71KB | lodash-es with tree-shaking |
| axios | 14KB | Native fetch or ky (3KB) |
| jquery | 87KB | Native DOM APIs |
| @mui/material | Large | shadcn/ui or Radix UI |

---

## React Patterns

Reference: `references/react_patterns.md`

### Compound Components

Share state between related components:

```tsx
const Tabs = ({ children }) => {
  const [active, setActive] = useState(0);
  return (
    <TabsContext.Provider value={{ active, setActive }}>
      {children}
    </TabsContext.Provider>
  );
};

Tabs.List = TabList;
Tabs.Panel = TabPanel;

// Usage
<Tabs>
  <Tabs.List>
    <Tabs.Tab>One</Tabs.Tab>
    <Tabs.Tab>Two</Tabs.Tab>
  </Tabs.List>
  <Tabs.Panel>Content 1</Tabs.Panel>
  <Tabs.Panel>Content 2</Tabs.Panel>
</Tabs>
```

### Custom Hooks

Extract reusable logic:

```tsx
function useDebounce<T>(value: T, delay = 500): T {
  const [debouncedValue, setDebouncedValue] = useState(value);

  useEffect(() => {
    const timer = setTimeout(() => setDebouncedValue(value), delay);
    return () => clearTimeout(timer);
  }, [value, delay]);

  return debouncedValue;
}

// Usage
const debouncedSearch = useDebounce(searchTerm, 300);
```

### Render Props

Share rendering logic:

```tsx
function DataFetcher({ url, render }) {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    fetch(url).then(r => r.json()).then(setData).finally(() => setLoading(false));
  }, [url]);

  return render({ data, loading });
}

// Usage
<DataFetcher
  url="/api/users"
  render={({ data, loading }) =>
    loading ? <Spinner /> : <UserList users={data} />
  }
/>
```

---

## Next.js Optimization

Reference: `references/nextjs_optimization_guide.md`

### Server vs Client Components

Use Server Components by default. Add 'use client' only when you need:
- Event handlers (onClick, onChange)
- State (useState, useReducer)
- Effects (useEffect)
- Browser APIs

```tsx
// Server Component (default) - no 'use client'
async function ProductPage({ params }) {
  const product = await getProduct(params.id);  // Server-side fetch

  return (
    <div>
      <h1>{product.name}</h1>
      <AddToCartButton productId={product.id} />  {/* Client component */}
    </div>
  );
}

// Client Component
'use client';
function AddToCartButton({ productId }) {
  const [adding, setAdding] = useState(false);
  return <button onClick={() => addToCart(productId)}>Add</button>;
}
```

### Image Optimization

```tsx
import Image from 'next/image';

// Above the fold - load immediately
<Image
  src="/hero.jpg"
  alt="Hero"
  width={1200}
  height={600}
  priority
/>

// Responsive image with fill
<div className="relative aspect-video">
  <Image
    src="/product.jpg"
    alt="Product"
    fill
    sizes="(max-width: 768px) 100vw, 50vw"
    className="object-cover"
  />
</div>
```

### Data Fetching Patterns

```tsx
// Parallel fetching
async function Dashboard() {
  const [user, stats] = await Promise.all([
    getUser(),
    getStats()
  ]);
  return <div>...</div>;
}

// Streaming with Suspense
async function ProductPage({ params }) {
  return (
    <div>
      <ProductDetails id={params.id} />
      <Suspense fallback={<ReviewsSkeleton />}>
        <Reviews productId={params.id} />
      </Suspense>
    </div>
  );
}
```

---

## Accessibility and Testing

Reference: `references/frontend_best_practices.md`

### Accessibility Checklist

1. **Semantic HTML**: Use proper elements (`<button>`, `<nav>`, `<main>`)
2. **Keyboard Navigation**: All interactive elements focusable
3. **ARIA Labels**: Provide labels for icons and complex widgets
4. **Color Contrast**: Minimum 4.5:1 for normal text
5. **Focus Indicators**: Visible focus states

```tsx
// Accessible button
<button
  type="button"
  aria-label="Close dialog"
  onClick={onClose}
  className="focus-visible:ring-2 focus-visible:ring-blue-500"
>
  <XIcon aria-hidden="true" />
</button>

// Skip link for keyboard users
<a href="#main-content" className="sr-only focus:not-sr-only">
  Skip to main content
</a>
```

### Testing Strategy

```tsx
// Component test with React Testing Library
import { render, screen } from '@testing-library/react';
import userEvent from '@testing-library/user-event';

test('button triggers action on click', async () => {
  const onClick = vi.fn();
  render(<Button onClick={onClick}>Click me</Button>);

  await userEvent.click(screen.getByRole('button'));
  expect(onClick).toHaveBeenCalledTimes(1);
});

// Test accessibility
test('dialog is accessible', async () => {
  render(<Dialog open={true} title="Confirm" />);

  expect(screen.getByRole('dialog')).toBeInTheDocument();
  expect(screen.getByRole('dialog')).toHaveAttribute('aria-labelledby');
});
```

---

## Quick Reference

### Common Next.js Config

```js
// next.config.js
const nextConfig = {
  images: {
    remotePatterns: [{ hostname: 'cdn.example.com' }],
    formats: ['image/avif', 'image/webp'],
  },
  experimental: {
    optimizePackageImports: ['lucide-react', '@heroicons/react'],
  },
};
```

### Tailwind CSS Utilities

```tsx
// Conditional classes with cn()
import { cn } from '@/lib/utils';

<button className={cn(
  'px-4 py-2 rounded',
  variant === 'primary' && 'bg-blue-500 text-white',
  disabled && 'opacity-50 cursor-not-allowed'
)} />
```

### TypeScript Patterns

```tsx
// Props with children
interface CardProps {
  className?: string;
  children: React.ReactNode;
}

// Generic component
interface ListProps<T> {
  items: T[];
  renderItem: (item: T) => React.ReactNode;
}

function List<T>({ items, renderItem }: ListProps<T>) {
  return <ul>{items.map(renderItem)}</ul>;
}
```

---

## Resources

- React Patterns: `references/react_patterns.md`
- Next.js Optimization: `references/nextjs_optimization_guide.md`
- Best Practices: `references/frontend_best_practices.md`

---

## Troubleshooting

| Problem | Cause | Solution |
|---------|-------|----------|
| Scaffolder fails with "Directory already exists" | Target project folder already present on disk | Delete or rename the existing directory, or choose a different project name |
| Component generator creates PascalCase name from kebab-case incorrectly | Input contains mixed delimiters (e.g., `my_comp-name`) | Use consistent kebab-case (`my-comp-name`) or PascalCase (`MyCompName`) as input |
| Bundle analyzer reports "No valid package.json found" | Script is pointed at a directory without `package.json` or the file has invalid JSON | Pass the correct project root directory; validate `package.json` syntax with `python -m json.tool package.json` |
| `--dry-run` shows files but `--features` content is listed as TODO | Feature file content keys are not mapped in `FILE_CONTENTS` dictionary | This is expected for some add-on features; implement the placeholder files manually after scaffolding |
| Bundle score unexpectedly low despite few dependencies | Dev-only packages (TypeScript, ESLint, Tailwind) are listed under `dependencies` instead of `devDependencies` | Move build/dev tooling to `devDependencies` in `package.json` |
| Import analysis returns zero files checked | Source code is not in `src/`, `app/`, or `pages/` directories | Run with `--verbose` and ensure your source files live in one of the three expected directories |
| Generated component missing `'use client'` directive | Component was generated with `--type server` instead of the default `client` type | Re-run with `--type client` or add the `'use client'` directive manually at the top of the file |

---

## Success Criteria

- **Lighthouse performance score above 90** on the generated project's production build, indicating Server Components and image optimization are configured correctly.
- **Bundle size under 200KB gzipped** for the initial JavaScript payload, validated by running the bundle analyzer with a grade of A or B.
- **Zero heavy-dependency warnings** from `bundle_analyzer.py` after applying all recommended replacements.
- **Component generation time under 2 seconds** per component, including test and story file creation.
- **All generated TypeScript files pass `tsc --noEmit`** without errors, confirming type-safe scaffolding output.
- **Accessibility audit produces zero critical violations** when running axe-core or Lighthouse accessibility checks against generated components.
- **Test coverage above 80%** for generated components when the `--with-test` flag is used and tests are executed with Vitest.

---

## Scope & Limitations

**What this skill covers:**
- React and Next.js project scaffolding with TypeScript and Tailwind CSS
- Component, hook, test, and Storybook story generation following established patterns
- Static bundle analysis based on `package.json` dependency inspection and import pattern scanning
- Frontend-specific best practices for Server Components, image optimization, data fetching, and accessibility

**What this skill does NOT cover:**
- Backend API development, database schema design, or server infrastructure -- see **senior-backend** and **senior-fullstack**
- End-to-end testing with Cypress or Playwright -- see **senior-qa**
- CI/CD pipeline configuration and Docker deployment -- see **senior-devops**
- Security vulnerability scanning and penetration testing -- see **senior-secops** and **senior-security**

---

## Integration Points

| Skill | Integration | Data Flow |
|-------|-------------|-----------|
| **senior-fullstack** | Scaffolded frontend projects connect to fullstack project scaffolder for API layer setup | Frontend project structure feeds into `project_scaffolder.py` which adds backend, Docker, and CI/CD layers |
| **senior-backend** | Components consuming API data follow patterns defined by backend skill's REST/GraphQL conventions | Backend API response types imported into frontend `types/` directory generated by this skill |
| **senior-qa** | Generated test files (`--with-test`) use the same Testing Library conventions that the QA skill's test strategies build upon | Component test files hand off to QA skill for integration and E2E test coverage expansion |
| **senior-devops** | Bundle analyzer output informs build pipeline optimization decisions | Bundle health score and dependency warnings feed into CI quality gates configured by DevOps skill |
| **senior-secops** | Dependency analysis identifies packages that need security audit | Heavy/outdated dependency warnings from `bundle_analyzer.py` trigger security review workflows |
| **code-reviewer** | Generated components follow patterns that the code reviewer skill validates | Code reviewer checks generated components against React/TypeScript best practices defined in this skill's references |

---

## Tool Reference

### frontend_scaffolder.py

- **Purpose**: Scaffold a complete Next.js or React project with TypeScript, Tailwind CSS, and optional feature modules.
- **Usage**: `python scripts/frontend_scaffolder.py <name> [flags]`
- **Flags**:

| Flag | Type | Default | Description |
|------|------|---------|-------------|
| `name` | positional | (required) | Project name, kebab-case recommended |
| `--dir`, `-d` | string | `.` | Output directory where the project folder is created |
| `--template`, `-t` | choice | `nextjs` | Project template: `nextjs` or `react` |
| `--features`, `-f` | string | (none) | Comma-separated features: `auth`, `api`, `forms`, `testing`, `storybook` |
| `--list-templates` | flag | off | List available project templates and exit |
| `--list-features` | flag | off | List available feature modules and exit |
| `--dry-run` | flag | off | Preview generated file list without writing to disk |
| `--json` | flag | off | Output result as JSON instead of human-readable summary |

- **Example**:
  ```bash
  python scripts/frontend_scaffolder.py dashboard --template nextjs --features auth,api --json
  ```
  ```json
  {
    "name": "dashboard",
    "template": "nextjs",
    "template_name": "Next.js 14+ App Router",
    "features": ["auth", "api"],
    "path": "./dashboard",
    "files_created": 28,
    "next_steps": ["cd dashboard", "npm install", "npm run dev"]
  }
  ```
- **Output Formats**: Human-readable summary (default) or JSON (`--json`).

---

### component_generator.py

- **Purpose**: Generate React/Next.js component files with TypeScript, optional test, and Storybook story.
- **Usage**: `python scripts/component_generator.py <name> [flags]`
- **Flags**:

| Flag | Type | Default | Description |
|------|------|---------|-------------|
| `name` | positional | (required) | Component name in PascalCase or kebab-case |
| `--dir`, `-d` | string | `src/components` | Output directory for generated files |
| `--type`, `-t` | choice | `client` | Component type: `client`, `server`, or `hook` |
| `--with-test` | flag | off | Generate a `.test.tsx` file with Testing Library boilerplate |
| `--with-story` | flag | off | Generate a `.stories.tsx` file for Storybook |
| `--no-index` | flag | off | Skip generating the `index.ts` barrel export file |
| `--flat` | flag | off | Place files directly in output dir without creating a subdirectory |
| `--dry-run` | flag | off | Preview what would be generated without writing files |
| `--verbose`, `-v` | flag | off | Enable verbose output |

- **Example**:
  ```bash
  python scripts/component_generator.py ProductCard --dir src/components/ui --type client --with-test --with-story
  ```
  ```
  ==================================================
  Component Generated: ProductCard
  ==================================================
  Type: client
  Directory: src/components/ui/ProductCard

  Files created:
    - src/components/ui/ProductCard/ProductCard.tsx
    - src/components/ui/ProductCard/ProductCard.test.tsx
    - src/components/ui/ProductCard/ProductCard.stories.tsx
    - src/components/ui/ProductCard/index.ts
  ==================================================
  ```
- **Output Formats**: Human-readable summary only.

---

### bundle_analyzer.py

- **Purpose**: Analyze `package.json` and project source files for bundle size issues, heavy dependencies, and optimization opportunities.
- **Usage**: `python scripts/bundle_analyzer.py [project_dir] [flags]`
- **Flags**:

| Flag | Type | Default | Description |
|------|------|---------|-------------|
| `project_dir` | positional | `.` | Project directory containing `package.json` |
| `--json` | flag | off | Output full analysis as JSON |
| `--verbose`, `-v` | flag | off | Include detailed import pattern analysis across `src/`, `app/`, and `pages/` directories |

- **Example**:
  ```bash
  python scripts/bundle_analyzer.py /path/to/my-app --verbose
  ```
  ```
  ============================================================
  FRONTEND BUNDLE ANALYSIS REPORT
  ============================================================

  Bundle Health Score: 70/100 (C)

  Dependencies: 12 production, 18 dev

  --- HEAVY DEPENDENCIES ---

    moment (290KB)
      Reason: Large locale files bundled by default
      Alternative: date-fns (12KB) or dayjs (2KB)

    lodash (71KB)
      Reason: Full library often imported when only few functions needed
      Alternative: lodash-es with tree-shaking or individual imports (lodash/get)

  --- IMPORT ISSUES ---
    - src/utils/date.ts: Consider replacing moment with date-fns or dayjs

  --- RECOMMENDATIONS ---
    1. Replace heavy dependencies with lighter alternatives
  ============================================================
  ```
- **Output Formats**: Human-readable report (default) or JSON (`--json`).