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

// 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 /> : error ? <ErrorMessage error={error} /> : <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

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

This example assumes cn is an existing class merging helper (see the Tailwind Merge Utility section in the CSS styling reference) and that Spinner is an existing project component. Reuse the helpers and components the project already has, and ask the user before adding new files or packages to supply them.

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)}
      {...props}
      disabled={isLoading || props.disabled}
    >
      {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)} aria-expanded={isOpen} 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, type Ref } 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
// In a separate child component, props holds that component's declared id
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

1. Single Responsibility: Each component does one thing well
2. Prop Drilling Prevention: Use context for deeply nested data
3. Accessible by Default: Include ARIA attributes, keyboard support
4. Controlled vs Uncontrolled: Support both patterns when appropriate
5. Forward Refs: Allow parent access to DOM nodes
6. Memoization: Use React.memo, useMemo for expensive renders
7. 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