Building Compound Components

Create unstyled, composable React components following the Radix UI / Base UI pattern. Components expose behavior via context while consumers control rendering.

Quick Start

tsx

// 1. Create context for shared state
const StepsContext = React.createContext<StepsContextValue | null>(null);

// 2. Create Root that provides context
const StepsRoot = ({ children, className, ...props }) => {
  const [steps] = useState(["Step 1", "Step 2"]);
  return (
    <StepsContext.Provider value={{ steps }}>
      <div className={className} {...props}>
        {children}
      </div>
    </StepsContext.Provider>
  );
};

// 3. Create consumer components
const StepsItem = ({ children, className, ...props }) => {
  const { steps } = useStepsContext();
  return (
    <div className={className} {...props}>
      {children}
    </div>
  );
};

// 4. Export as namespace
export const Steps = {
  Root: StepsRoot,
  Item: StepsItem,
};

Core Pattern

File Structure

code

my-component/
├── index.tsx              # Namespace export
├── root/
│   ├── component-root.tsx
│   └── component-context.tsx
├── item/
│   └── component-item.tsx
└── content/
    └── component-content.tsx

Context Pattern

tsx

// component-context.tsx
import * as React from "react";

interface ComponentContextValue {
  data: unknown;
  isOpen: boolean;
  toggle: () => void;
}

const ComponentContext = React.createContext<ComponentContextValue | null>(
  null,
);

export function useComponentContext() {
  const context = React.useContext(ComponentContext);
  if (!context) {
    throw new Error("Component parts must be used within Component.Root");
  }
  return context;
}

export { ComponentContext };

Root Component

tsx

// component-root.tsx
import { Slot } from "@radix-ui/react-slot";
import * as React from "react";
import { ComponentContext } from "./component-context";

interface ComponentRootProps extends React.HTMLAttributes<HTMLDivElement> {
  asChild?: boolean;
  defaultOpen?: boolean;
}

export const ComponentRoot = React.forwardRef<
  HTMLDivElement,
  ComponentRootProps
>(({ asChild, defaultOpen = false, children, ...props }, ref) => {
  const [isOpen, setIsOpen] = React.useState(defaultOpen);
  const Comp = asChild ? Slot : "div";

  return (
    <ComponentContext.Provider
      value={{ isOpen, toggle: () => setIsOpen(!isOpen) }}
    >
      <Comp ref={ref} data-state={isOpen ? "open" : "closed"} {...props}>
        {children}
      </Comp>
    </ComponentContext.Provider>
  );
});
ComponentRoot.displayName = "Component.Root";

Namespace Export

tsx

// index.tsx
import { ComponentRoot } from "./root/component-root";
import { ComponentTrigger } from "./trigger/component-trigger";
import { ComponentContent } from "./content/component-content";

export const Component = {
  Root: ComponentRoot,
  Trigger: ComponentTrigger,
  Content: ComponentContent,
};

// Re-export types
export type { ComponentRootProps } from "./root/component-root";
export type { ComponentContentProps } from "./content/component-content";

Composition Patterns

Pattern 1: Direct Children (Simplest)

Best for static content. Consumer just adds children.

tsx

// Component
const Content = ({ children, className, ...props }) => {
  const { data } = useContext();
  return (
    <div className={className} {...props}>
      {children}
    </div>
  );
};

// Usage
<Component.Content className="my-styles">
  <p>Static content here</p>
</Component.Content>;

Pattern 2: Render Prop (State Access)

Best when consumer needs internal state.

tsx

// Component
interface ContentProps {
  render?: (props: { data: string; isLoading: boolean }) => React.ReactNode;
  children?: React.ReactNode;
}

const Content = ({ render, children, ...props }) => {
  const { data, isLoading } = useContext();

  const content = render ? render({ data, isLoading }) : children;
  return <div {...props}>{content}</div>;
};

// Usage
<Component.Content
  render={({ data, isLoading }) => (
    <div className={isLoading ? "opacity-50" : ""}>{data}</div>
  )}
/>;

Pattern 3: Sub-Context (Maximum Composability)

Best for lists/iterations where each item needs its own context.

tsx

// Parent provides array context
const Steps = ({ children }) => {
  const { reasoning } = useMessageContext();
  return (
    <StepsContext.Provider value={{ steps: reasoning }}>
      {children}
    </StepsContext.Provider>
  );
};

// Item provides individual step context
const Step = ({ children, index }) => {
  const { steps } = useStepsContext();
  return (
    <StepContext.Provider value={{ step: steps[index], index }}>
      {children}
    </StepContext.Provider>
  );
};

// Content reads from nearest context
const StepContent = ({ className }) => {
  const { step } = useStepContext();
  return <div className={className}>{step}</div>;
};

// Usage - maximum flexibility
<ReasoningInfo.Steps className="space-y-4">
  {steps.map((_, i) => (
    <ReasoningInfo.Step key={i} index={i}>
      <div className="custom-wrapper">
        <ReasoningInfo.StepContent className="text-sm" />
      </div>
    </ReasoningInfo.Step>
  ))}
</ReasoningInfo.Steps>;

Essential Features

1. Data Attributes for CSS Styling

Expose state via data attributes so consumers can style with CSS only:

tsx

<div
  data-state={isOpen ? "open" : "closed"}
  data-disabled={disabled || undefined}
  data-loading={isLoading || undefined}
  data-slot="component-trigger"
  {...props}
>

CSS targeting:

css

[data-state="open"] {
  /* open styles */
}
[data-slot="component-trigger"]:hover {
  /* hover styles */
}

2. asChild Pattern (Radix Slot)

Allow consumers to replace the default element:

tsx

import { Slot } from "@radix-ui/react-slot";

interface Props extends React.HTMLAttributes<HTMLButtonElement> {
  asChild?: boolean;
}

const Trigger = ({ asChild, ...props }) => {
  const Comp = asChild ? Slot : "button";
  return <Comp {...props} />;
};

// Usage
<Component.Trigger asChild>
  <a href="/link">I'm a link now</a>
</Component.Trigger>;

3. Ref Forwarding

Always forward refs for DOM access:

tsx

export const Component = React.forwardRef<HTMLDivElement, Props>(
  (props, ref) => {
    return <div ref={ref} {...props} />;
  },
);
Component.displayName = "Component";

4. Proper TypeScript

Export prop types for consumers:

tsx

export interface ComponentRootProps extends React.HTMLAttributes<HTMLDivElement> {
  asChild?: boolean;
  defaultOpen?: boolean;
}

export interface ComponentContentRenderProps {
  data: string;
  isLoading: boolean;
}

Guidelines

•No styles in primitives - consumers control all styling via className/props
•Context for state sharing - parent manages, children consume
•Data attributes for CSS - expose state like data-state="open"
•Support asChild - let consumers swap the underlying element
•Forward refs - always use forwardRef
•Display names - set for React DevTools (Component.Root, Component.Item)
•Throw on missing context - fail fast with clear error messages
•Export types - consumers need ComponentProps, RenderProps types

When to Use Each Pattern

Scenario	Pattern	Why
Static content	Direct children	Simplest, most flexible
Need internal state	Render prop	Explicit state access
List/iteration	Sub-context	Each item gets own context
Element polymorphism	asChild	Change underlying element
CSS-only styling	Data attributes	No JS needed for style variants

Anti-Patterns

•Hardcoded styles - primitives should be unstyled
•Prop drilling - use context instead
•Missing error boundaries - throw when context is missing
•Inline functions in render prop types - define proper interfaces
•Default exports - use named exports in namespace object