Senior Frontend

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

Table of Contents

• Project Scaffolding
• Component Generation
• Bundle Analysis
• React Patterns
• Next.js Optimization
• 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:

   bashCopy

   python scripts/frontend_scaffolder.py my-app --template nextjs
   

2. Add optional features (auth, api, forms, testing, storybook):

   bashCopy

   python scripts/frontend_scaffolder.py dashboard --template nextjs --features auth,api
   

3. Navigate to the project and install dependencies:

   bashCopy

   cd my-app && npm install
   

4. Start the development server:

   bashCopy

   npm run dev
   

Scaffolder Options

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:

   bashCopy

   python scripts/component_generator.py Button --dir src/components/ui
   

2. Generate a server component:

   bashCopy

   python scripts/component_generator.py ProductCard --type server
   

3. Generate with test and story files:

   bashCopy

   python scripts/component_generator.py UserProfile --with-test --with-story
   

4. Generate a custom hook:

   bashCopy

   python scripts/component_generator.py FormValidation --type hook
   

Generator Options

Generated Component Example

'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:

   bashCopy

   python scripts/bundle_analyzer.py /path/to/project
   

2. Review the health score and issues:

   Copy

   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:

   bashCopy

   python scripts/bundle_analyzer.py . --verbose
   

Bundle Score Interpretation

Heavy Dependencies Detected

The analyzer identifies these common heavy packages:

React Patterns

Reference: references/react_patterns.md

Compound Components

Share state between related components:

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:

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:

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

// 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

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

// 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

// 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

// 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

// 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

// 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

// 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

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

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:

• Example:
  bashCopy

  python scripts/frontend_scaffolder.py dashboard --template nextjs --features auth,api --json
  

  jsonCopy

  {
    "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:

• Example:
  bashCopy

  python scripts/component_generator.py ProductCard --dir src/components/ui --type client --with-test --with-story
  

  Copy

  ==================================================
  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:

• Example:
  bashCopy

  python scripts/bundle_analyzer.py /path/to/my-app --verbose
  

  Copy

  ============================================================
  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).