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

// 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

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

Slots (Vue/Svelte): Named content injection points

<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

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

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(buttonVariants({ variant, size }), className)}
      disabled={isLoading || props.disabled}
      {...props}
    >
      {isLoading && <Spinner className="mr-2 h-4 w-4" />}
      {children}
    </button>
  ),
);
Button.displayName = "Button";

Framework Patterns

React: Compound Components

import { createContext, useContext, useState, type ReactNode } from "react";

interface AccordionContextValue {
  openItems: Set<string>;
  toggle: (id: string) => void;
}

const AccordionContext = createContext<AccordionContextValue | null>(null);

function useAccordion() {
  const context = useContext(AccordionContext);
  if (!context) throw new Error("Must be used within Accordion");
  return context;
}

export function Accordion({ children }: { children: ReactNode }) {
  const [openItems, setOpenItems] = useState<Set<string>>(new Set());

  const toggle = (id: string) => {
    setOpenItems((prev) => {
      const next = new Set(prev);
      next.has(id) ? next.delete(id) : next.add(id);
      return next;
    });
  };

  return (
    <AccordionContext.Provider value={{ openItems, toggle }}>
      <div className="divide-y">{children}</div>
    </AccordionContext.Provider>
  );
}

Accordion.Item = function AccordionItem({
  id,
  title,
  children,
}: {
  id: string;
  title: string;
  children: ReactNode;
}) {
  const { openItems, toggle } = useAccordion();
  const isOpen = openItems.has(id);

  return (
    <div>
      <button onClick={() => toggle(id)} className="w-full text-left py-3">
        {title}
      </button>
      {isOpen && <div className="pb-3">{children}</div>}
    </div>
  );
};

Vue 3: Composables

<script setup lang="ts">
import { ref, computed, provide, inject, type InjectionKey } from "vue";

interface TabsContext {
  activeTab: Ref<string>;
  setActive: (id: string) => void;
}

const TabsKey: InjectionKey<TabsContext> = Symbol("tabs");

// Parent component
const activeTab = ref("tab-1");
provide(TabsKey, {
  activeTab,
  setActive: (id: string) => {
    activeTab.value = id;
  },
});

// Child component usage
const tabs = inject(TabsKey);
const isActive = computed(() => tabs?.activeTab.value === props.id);
</script>

Svelte 5: Runes

<script lang="ts">
  interface Props {
    variant?: 'primary' | 'secondary';
    size?: 'sm' | 'md' | 'lg';
    onclick?: () => void;
    children: import('svelte').Snippet;
  }

  let { variant = 'primary', size = 'md', onclick, children }: Props = $props();

  const classes = $derived(
    `btn btn-${variant} btn-${size}`
  );
</script>

<button class={classes} {onclick}>
  {@render children()}
</button>

Best Practices

Single Responsibility: Each component does one thing well
Prop Drilling Prevention: Use context for deeply nested data
Accessible by Default: Include ARIA attributes, keyboard support
Controlled vs Uncontrolled: Support both patterns when appropriate
Forward Refs: Allow parent access to DOM nodes
Memoization: Use React.memo, useMemo for expensive renders
Error Boundaries: Wrap components that may fail

Common Issues

Prop Explosion: Too many props - consider composition instead
Style Conflicts: Use scoped styles or CSS Modules
Re-render Cascades: Profile with React DevTools, memo appropriately
Accessibility Gaps: Test with screen readers and keyboard navigation
Bundle Size: Tree-shake unused component variants

web-component-design