Web Component Design

# Web Component Design

Build reusable, maintainable UI components using modern frameworks with clean composition patterns and styling approaches.

## When to Use This Skill

- Designing reusable component libraries or design systems
- Implementing complex component composition patterns
- Choosing and applying CSS-in-JS solutions
- Building accessible, responsive UI components
- Creating consistent component APIs across a codebase
- Refactoring legacy components into modern patterns
- Implementing compound components or render props

## Core Concepts

### 1. Component Composition Patterns

**Compound Components**: Related components that work together

```tsx
// Usage
<Select value={value} onChange={setValue}>
  <Select.Trigger>Choose option</Select.Trigger>
  <Select.Options>
    <Select.Option value="a">Option A</Select.Option>
    <Select.Option value="b">Option B</Select.Option>
  </Select.Options>
</Select>
```

**Render Props**: Delegate rendering to parent

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

**Slots (Vue/Svelte)**: Named content injection points

```vue
<template>
  <Card>
    <template #header>Title</template>
    <template #content>Body text</template>
    <template #footer><Button>Action</Button></template>
  </Card>
</template>
```

### 2. CSS-in-JS Approaches

| Solution              | Approach               | Best For                          |
| --------------------- | ---------------------- | --------------------------------- |
| **Tailwind CSS**      | Utility classes        | Rapid prototyping, design systems |
| **CSS Modules**       | Scoped CSS files       | Existing CSS, gradual adoption    |
| **styled-components** | Template literals      | React, dynamic styling            |
| **Emotion**           | Object/template styles | Flexible, SSR-friendly            |
| **Vanilla Extract**   | Zero-runtime           | Performance-critical apps         |

### 3. Component API Design

```tsx
interface ButtonProps {
  variant?: "primary" | "secondary" | "ghost";
  size?: "sm" | "md" | "lg";
  isLoading?: boolean;
  isDisabled?: boolean;
  leftIcon?: React.ReactNode;
  rightIcon?: React.ReactNode;
  children: React.ReactNode;
  onClick?: () => void;
}
```

**Principles**:

- Use semantic prop names (`isLoading` vs `loading`)
- Provide sensible defaults
- Support composition via `children`
- Allow style overrides via `className` or `style`

## Quick Start: React Component with Tailwind

```tsx
import { forwardRef, type ComponentPropsWithoutRef } from "react";
import { cva, type VariantProps } from "class-variance-authority";
import { cn } from "@/lib/utils";

const buttonVariants = cva(
  "inline-flex items-center justify-center rounded-md font-medium transition-colors focus-visible:outline-none focus-visible:ring-2 disabled:pointer-events-none disabled:opacity-50",
  {
    variants: {
      variant: {
        primary: "bg-blue-600 text-white hover:bg-blue-700",
        secondary: "bg-gray-100 text-gray-900 hover:bg-gray-200",
        ghost: "hover:bg-gray-100 hover:text-gray-900",
      },
      size: {
        sm: "h-8 px-3 text-sm",
        md: "h-10 px-4 text-sm",
        lg: "h-12 px-6 text-base",
      },
    },
    defaultVariants: {
      variant: "primary",
      size: "md",
    },
  },
);

interface ButtonProps
  extends
    ComponentPropsWithoutRef<"button">,
    VariantProps<typeof buttonVariants> {
  isLoading?: boolean;
}

export const Button = forwardRef<HTMLButtonElement, ButtonProps>(
  ({ className, variant, size, isLoading, children, ...props }, ref) => (
    <button
      ref={ref}
      className={cn