React SPA Development Pattern

This skill provides guidelines for developing React Single Page Applications following a specific architecture pattern, primarily used for small demo applications.

When to Use This Skill

Use this skill when:

Building a new React SPA from scratch
Working on an existing React SPA project
The user mentions they want a React app following their standard pattern

Project Setup

When scaffolding a new React SPA project, refer to PROJECT_SETUP.md for:

Gathering project information (name, description, version)
Complete dependency list with latest versions
Full project structure
All configuration files (vite, TypeScript, ESLint, Prettier, git)
Initial source files

Project Structure

src/
├── components/           # App-specific components with logic
├── theme/
│   └── index.ts         # Central export for all theme components
├── utils/
│   └── classnames.ts    # CN utility for conditional classes
├── App.tsx              # Root component
├── index.css            # Tailwind v4 theme + animations
├── main.tsx             # React entry point
└── vite-env.d.ts        # Vite type declarations

Component Organization

Components (`src/components/`)

App-specific components with business logic:

Contains components tied to the application's functionality
Should be grouped in folders where it makes sense (e.g., components/auth/, components/dashboard/)
One default export per component file
Can use state, side effects, and complex logic

Example structure:

components/
├── auth/
│   ├── LoginForm.tsx
│   └── RegisterForm.tsx
├── dashboard/
│   └── MetricCard.tsx
└── LanguageSelector.tsx

Theme Components (`src/theme/`)

Reusable UI components with minimal logic:

Generic, reusable UI elements (buttons, inputs, cards, etc.)
Rarely contain business logic (but can if needed)
Must always be imported/exported through src/theme/index.ts
Organized in subfolders by component type

Example theme component:

// src/theme/button/Button.tsx
import type { ButtonHTMLAttributes } from "react";
import cn from "../../utils/classnames";

interface ButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
  variant?: "primary" | "secondary";
  className?: string;
}

export default function Button({
  variant = "primary",
  className = "",
  children,
  ...props
}: ButtonProps) {
  return (
    <button
      className={cn(
        "px-4 py-2 rounded",
        {
          "bg-blue-500 text-white": variant === "primary",
          "bg-gray-200 text-black": variant === "secondary",
        },
        className
      )}
      {...props}
    >
      {children}
    </button>
  );
}

Central theme export:

// src/theme/index.ts

export { default as Button } from "./button/Button";
export { default as InputText } from "./form/InputText";

Usage in components:

import { Button, InputText } from "./theme";

export default function MyComponent() {
  return (
    <div>
      <InputText placeholder="Enter name" />
      <Button variant="primary">Submit</Button>
    </div>
  );
}

Utilities (`src/utils/`)

Utility files export multiple helper functions:

Pure functions without side effects
Group related utilities in the same file
Use named exports for utilities

Examples:

utils/classnames.ts - CN utility for conditional classes (required)
utils/format.ts - formatDate(), formatNumber(), formatCurrency()
utils/validation.ts - isEmail(), isValidUrl(), validateForm()

React Component Pattern

Standard structure for all React components:

import { useState } from "react";
import cn from "./utils/classnames";
import { Button } from "./theme";

interface MyComponentProps {
  title: string;
  count?: number;
  className?: string;
  onSubmit?: (value: string) => void;
}

export default function MyComponent({
  title,
  count = 0,
  className = "",
  onSubmit,
}: MyComponentProps) {
  const [value, setValue] = useState<string>("");

  const handleSubmit = () => {
    if (onSubmit) {
      onSubmit(value);
    }
  };

  return (
    <div className={cn("container", className)}>
      <h2>{title}</h2>
      <p>Count: {count}</p>
      <Button onClick={handleSubmit}>Submit</Button>
    </div>
  );
}

Key patterns:

One default export per component
TypeScript interface for props (suffix with Props)
Always include className?: string in props for styling flexibility
Destructure props with default values in function signature
Use cn() utility for combining classnames
Import theme components from "./theme"
Early returns for conditional rendering

TypeScript Guidelines

Type Safety Rules

Strict mode enabled - Use strict compiler options
Explicit types - Define interfaces for all component props and function parameters
No any - Use proper types or unknown with type guards
Type imports - Import types separately: import type { MyType } from './types'
Const assertions - Use as const for literal types instead of enums
Interface over type - Prefer interface for object shapes

Common Patterns

IMPORTANT: Never use React. prefix for types. Always import types directly from React.

import type { 
  ButtonHTMLAttributes, 
  InputHTMLAttributes,
  MouseEvent,
  ReactNode 
} from "react";

// ✓ Correct: Import types and extend without React. prefix
interface ButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
  variant?: "primary" | "secondary";
}

// ✗ Wrong: Don't use React. prefix
interface ButtonProps extends React.ButtonHTMLAttributes<HTMLButtonElement> {
  variant?: "primary" | "secondary";
}

// ✓ Event handlers
const handleClick = (event: MouseEvent<HTMLButtonElement>) => {
  // ...
};

// ✓ Refs
const inputRef = useRef<HTMLInputElement>(null);

// ✓ Children prop
interface ContainerProps {
  children: ReactNode;
}

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

React Patterns

Component Guidelines

Functional components only - No class components
React hooks - Use useState, useEffect, useRef, useMemo, useCallback
Props destructuring - Destructure props in function signature with defaults
Default exports - Components use default export, utilities use named exports
Single responsibility - Keep components focused on one task
Composition over inheritance - Build complex UIs from simple components

State Management

Local state first - Use useState for component-specific state
Props drilling - Pass state down explicitly, avoid global state unless needed
Lift state up - Move state to common ancestor when multiple components need it
Form libraries - Use react-hook-form for complex forms
URL state - Use URL hash/query params for shareable state

Common Hooks Patterns

// State with derived values
const [items, setItems] = useState<Item[]>([]);
const activeItems = items.filter((item) => item.active);

// Effect with cleanup
useEffect(() => {
  const subscription = api.subscribe();
  return () => subscription.unsubscribe();
}, []);

// Memoized expensive computation
const sortedItems = useMemo(
  () => items.sort((a, b) => a.name.localeCompare(b.name)),
  [items]
);

// Memoized callback
const handleClick = useCallback(() => {
  console.log(value);
}, [value]);

// Refs for DOM access
const inputRef = useRef<HTMLInputElement>(null);
useEffect(() => {
  inputRef.current?.focus();
}, []);

File Naming Conventions

Components: PascalCase (e.g., LanguageSelector.tsx, MetricCard.tsx)
Utilities: camelCase (e.g., classnames.ts, format.ts, validation.ts)
Types: types.ts or index.ts in dedicated folders
Constants: constants.ts with SCREAMING_SNAKE_CASE exports

Examples:

src/
├── components/
│   ├── UserProfile.tsx          ✓ PascalCase
│   └── DashboardMetrics.tsx     ✓ PascalCase
├── theme/
│   └── button/
│       └── Button.tsx           ✓ PascalCase
├── utils/
│   ├── classnames.ts            ✓ camelCase
│   ├── format.ts                ✓ camelCase
│   └── validation.ts            ✓ camelCase
└── constants.ts                 ✓ camelCase

Code Style

General Formatting

Prettier formatting - Auto-format on save, follow .prettierrc rules
ESLint - Use TypeScript + React hooks + React Refresh plugins
Functional programming - Prefer immutable operations, map/filter over loops
Early returns - Use guard clauses to reduce nesting
Descriptive names - Clear variable/function names over comments

Import Order

Imports are automatically sorted using @trivago/prettier-plugin-sort-imports:

Configuration in .prettierrc:

{
  "importOrder": ["<THIRD_PARTY_MODULES>", "^[./]"],
  "plugins": ["@trivago/prettier-plugin-sort-imports"]
}

Result: Two groups separated by blank line:

// Group 1: Third-party modules (alphabetically sorted)
import { useState, useEffect } from "react";
import type { ButtonHTMLAttributes, ReactNode } from "react";
import { User, Settings } from "lucide-react";

// Group 2: Local imports (alphabetically sorted)
import { Button, InputText } from "./theme";
import UserCard from "./components/UserCard";
import type { UserData } from "./types";
import cn from "./utils/classnames";
import { formatDate } from "./utils/format";

Do not manually organize imports - let Prettier handle it automatically.

Conditional Rendering

// Early return for loading/error states
if (isLoading) return <LoadingSpinner />;
if (error) return <ErrorMessage error={error} />;

// Ternary for simple conditions
{isActive ? <ActiveIcon /> : <InactiveIcon />}

// Logical AND for conditional display
{showTitle && <h1>{title}</h1>}

// Complex conditions - extract to variable
const canSubmit = isValid && !isSubmitting && hasChanges;
return <Button disabled={!canSubmit}>Submit</Button>;

Tailwind CSS Usage

CSS-First Configuration (v4+)

All Tailwind configuration uses the new CSS-first approach in src/index.css:

@import "tailwindcss";

@theme {
  /* Custom theme variables */
  --color-primary: #3b82f6;
  --color-secondary: #64748b;
  
  /* Custom breakpoints, spacing, etc. */
}

Utility Classes

// Use cn() for conditional classes
<div className={cn(
  "px-4 py-2 rounded",
  { "bg-blue-500": isPrimary },
  { "bg-gray-200": !isPrimary },
  className
)} />

// Responsive design
<div className="text-sm md:text-base lg:text-lg" />

// State variants
<button className="hover:bg-blue-600 focus:ring-2 active:scale-95" />

Performance Patterns

Optimization Strategies

Singleton pattern - For expensive resources (API clients, model instances)
Lazy loading - Load heavy resources only when needed
Debouncing - For expensive operations (API calls, heavy computations)
Memoization - Use useMemo/useCallback for expensive renders
Code splitting - Use dynamic imports for large features

Examples

// Lazy loading components
const HeavyComponent = lazy(() => import("./HeavyComponent"));

<Suspense fallback={<Loading />}>
  <HeavyComponent />
</Suspense>

// Debouncing input
const [search, setSearch] = useState("");
const debouncedSearch = useMemo(
  () => debounce((value: string) => performSearch(value), 300),
  []
);

// Memoize expensive calculations
const filteredData = useMemo(
  () => data.filter((item) => item.category === category),
  [data, category]
);

Best Practices

Component Design

Keep components small - Aim for <200 lines per component
Extract reusable logic - Custom hooks for shared behavior
Props over configuration - Make components flexible through props
Accessibility - Use semantic HTML and ARIA attributes
Error boundaries - Wrap components that might fail

Code Organization

Group related files - Keep related components together
Consistent naming - Follow naming conventions strictly
Avoid deep nesting - Flatten component hierarchies
Clear separation - Keep theme components separate from app logic
Single source of truth - Don't duplicate state

Development Workflow

Type first - Define interfaces before implementation
Test locally - Use npm run dev for rapid iteration
Lint and format - Run npm run lint and npm run format before commits
Build verification - Run npm run build to catch build issues

Tech Stack Summary

Core Dependencies

React - UI framework
TypeScript - Type safety
Vite - Build tool and dev server
Tailwind CSS v4+ - Styling with CSS-first configuration
lucide-react - Icon components

Dev Tools

@tailwindcss/vite - Tailwind Vite plugin
@vitejs/plugin-react - Fast Refresh support
ESLint with TypeScript and React plugins
Prettier - Code formatting

Reference Documentation

PROJECT_SETUP.md - Complete scaffolding guide with all configuration files
about.md - Original notes and context

This skill enables building maintainable, performant React SPAs with a consistent architecture pattern and best practices.