senior-frontend – Design & UI skill for AI agents

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:

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

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

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

3. Navigate to the project and install dependencies:

   cd my-app && npm install
   

4. Start the development server:

   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:

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

2. Generate a server component:

   python scripts/component_generator.py ProductCard --type server
   

3. Generate with test and story files:

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

4. Generate a custom hook:

   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

'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:

   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:

   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:

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 trig

… (full content is in the download package)