Shadcn Components

shadcn/ui Components Skill

Patterns and best practices for using shadcn/ui components in this Next.js application.

Architecture Overview

core/components/ui/              # Base shadcn/ui components (62 total)
├── button.tsx                   # With variants (cva)
├── card.tsx                     # Compound component
├── form.tsx                     # React Hook Form integration
├── input.tsx                    # forwardRef pattern
└── ...

contents/themes/{theme}/components/  # Theme-specific extensions
└── custom-components/

When to Use This Skill

• Building UI with shadcn/ui components
• Creating custom components that extend shadcn/ui
• Implementing forms with validation
• Understanding variant and compound patterns
• Ensuring accessibility compliance

Available Components (62 total)

Primitives

Custom/Extended Components

Key Patterns

1. Compound Component Pattern

All compound components follow the Card pattern:

// Exports multiple related components
export { Card, CardHeader, CardFooter, CardTitle, CardDescription, CardContent }

// Usage
<Card>
  <CardHeader>
    <CardTitle>Title</CardTitle>
    <CardDescription>Description text</CardDescription>
  </CardHeader>
  <CardContent>
    Main content here
  </CardContent>
  <CardFooter>
    <Button>Action</Button>
  </CardFooter>
</Card>

Components using this pattern:

• Card, Dialog, Alert, Sheet, Popover
• Select, Accordion, Tabs, Command
• ContextMenu, DropdownMenu, Menubar
• Breadcrumb, Table, RadioGroup

2. Variant Pattern with cva()

import { cva, type VariantProps } from 'class-variance-authority'

const buttonVariants = cva(
  // Base classes
  "inline-flex items-center justify-center rounded-md text-sm font-medium",
  {
    variants: {
      variant: {
        default: "bg-primary text-primary-foreground hover:bg-primary/90",
        destructive: "bg-destructive text-destructive-foreground hover:bg-destructive/90",
        outline: "border border-input bg-background hover:bg-accent",
        secondary: "bg-secondary text-secondary-foreground hover:bg-secondary/80",
        ghost: "hover:bg-accent hover:text-accent-foreground",
        link: "text-primary underline-offset-4 hover:underline",
      },
      size: {
        default: "h-9 px-4 py-2",
        sm: "h-8 rounded-md px-3 text-xs",
        lg: "h-10 rounded-md px-8",
        icon: "h-9 w-9",
      },
    },
    defaultVariants: {
      variant: "default",
      size: "default",
    },
  }
)

// Component definition
interface ButtonProps
  extends React.ButtonHTMLAttributes<HTMLButtonElement>,
    VariantProps<typeof buttonVariants> {}

const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
  ({ className, variant, size, ...props }, ref) => (
    <button
      className={cn(buttonVariants({ variant, size, className }))}
      ref={ref}
      {...props}
    />
  )
)

Components using variants:

• Button (variant + size)
• Badge (variant)
• Alert (variant)
• Toggle (variant + size)
• Sheet (side)

3. forwardRef Pattern

const Input = React.forwardRef<
  HTMLInputElement,
  React.ComponentProps<"input">
>(({ className, type, ...props }, ref) => (
  <input
    type={type}
    className={cn(
      "flex h-9 w-full rounded-md border border-input bg-transparent px-3 py-1",
      "text-base shadow-sm transition-colors file:border-0",
      "placeholder:text-muted-foreground focus-visible:outline-none",
      "focus-visible:ring-1 focus-visible:ring-ring disabled:cursor-not-allowed",
      className
    )}
    ref={ref}
    {...props}
  />
))
Input.displayName = "Input"

4. cn() Utility

All components use cn() from @/core/lib/utils for class merging:

import { cn } from '@/core/lib/utils'

// Merges classes with Tailwind conflict resolution
className={cn(
  "base-tailwind-classes",
  isActive && "active-classes",
  className  // Props override
)}

Form Integration

Form Components

export {
  Form,           // = FormProvider from react-hook-form
  FormField,      // Controller wrapper with context
  FormItem,       // Layout wrapper with useId
  FormLabel,      // Accessible label with error styling
  FormControl,    // Slot-based control that adds ARIA attributes
  FormDescription,// Helper text
  FormMessage,    // Error message display
  useFormField    // Custom hook for field state
}

Complete Form Example

import { useForm } from 'react-hook-form'
import { zodResolver } from '@hookform/resolvers/zod'
import { z } from 'zod'
import {
  Form,
  FormControl,
  FormDescription,
  FormField,
  FormItem,
  FormLabel,
  FormMessage,
} from '@/core/components/ui/form'
import { Input } from '@/core/components/ui/input'
import { Button } from '@/core/components/ui/button'

const formSchema = z.object({
  name: z.string().min(2, 'Name must be at least 2 characters'),
  email: z.string().email('Invalid email address'),
})

type FormData = z.infer<typeof formSchema>

export function MyForm() {
  const form = useForm<FormData>({
    resolver: zodResolver(formSchema),
    defaultValues: {
      name: '',
      email: '',
    },
  })

  function onSubmit(data: FormData) {
    console.log(data)
  }

  return (
    <Form {...form}>
      <form className="space-y-4">
        <FormField
          control={form.control}
          name="name"
          render={({ field }) => (
            <FormItem>
              <FormLabel>Name</FormLabel>
              <FormControl>
                <Input
                  placeholder="Enter your name"
                  data-cy="name-input"
                  {...field}
                />
              </FormControl>
              <FormDescription>
                Your display name
              </FormDescription>
              <FormMessage />
            </FormItem>
          )}
        />

        <FormField
          control={form.control}
          name="email"
          render={({ field }) => (
            <FormItem>
              <FormLabel>Email</FormLabel>
              <FormControl>
                <Input
                  type="email"
                  placeholder="you@example.com"
                  data-cy="email-input"
                  {...field}
                />
              </FormControl>
              <FormMessage />
            </FormItem>
          )}
        />

        <Button type="submit" data-cy="submit-btn">
          Submit
        </Button>
      </form>
    </Form>
  )
}

data-cy Attributes

IMPORTANT: Core shadcn/ui components do NOT include data-cy attributes. They must be added at the usage layer.

// CORRECT - Add data-cy when using components
<Button
  data-cy="create-task-btn"
 
>
  Create Task
</Button>

<Input
  data-cy="task-title-input"
  placeholder="Task title"
  {...field}
/>

<Dialog>
  <DialogTrigger data-cy="open-dialog-btn">
    Open
  </DialogTrigger>
  <DialogContent data-cy="task-dialog">
    {/* ... */}
  </DialogContent>
</Dialog>

Accessibility

Built-in ARIA Support

// FormControl automatically adds:
<FormControl>
  {/* aria-invalid, aria-describedby */}
</FormControl>

// Dialog adds focus trap and escape handling
<Dialog>
  {/* role="dialog", aria-modal="true" */}
</Dialog>

// Select adds:
<Select>
  {/* role="combobox", aria-expanded */}
</Select>

Keyboard Navigation

All interactive components support:

• Tab - Navigate between elements
• Enter/Space - Activate buttons, toggles
• Escape - Close dialogs, popovers
• Arrow keys - Navigate lists, menus

Labels and Descriptions

<FormItem>
  <FormLabel htmlFor="email">Email</FormLabel>
  <FormControl>
    <Input id="email" aria-describedby="email-description" />
  </FormControl>
  <FormDescription id="email-description">
    We'll never share your email
  </FormDescription>
</FormItem>

Theming

CSS Variables

All components use CSS variables instead of hardcoded colors:

// CORRECT - Use semantic colors
className="bg-background text-foreground"
className="bg-primary text-primary-foreground"
className="bg-destructive text-destructive-foreground"
className="border-input"
className="ring-ring"

// WRONG - Hardcoded colors
className="bg-white text-black"
className="bg-blue-500 text-white"

Available Color Tokens

Common Patterns

Dialog with Form

<Dialog>
  <DialogTrigger asChild>
    <Button data-cy="open-create-dialog">Create New</Button>
  </DialogTrigger>
  <DialogContent data-cy="create-dialog">
    <DialogHeader>
      <DialogTitle>Create Item</DialogTitle>
      <DialogDescription>
        Fill in the details below
      </DialogDescription>
    </DialogHeader>
    <Form {...form}>
      <form
        {/* Form fields */}
        <DialogFooter>
          <Button type="submit" data-cy="submit-create">
            Create
          </Button>
        </DialogFooter>
      </form>
    </Form>
  </DialogContent>
</Dialog>

Dropdown Menu

<DropdownMenu>
  <DropdownMenuTrigger asChild>
    <Button variant="ghost" data-cy="actions-menu-btn">
      Actions
    </Button>
  </DropdownMenuTrigger>
  <DropdownMenuContent data-cy="actions-menu">
    <DropdownMenuLabel>Actions</DropdownMenuLabel>
    <DropdownMenuSeparator />
    <DropdownMenuItem data-cy="edit-action">
      Edit
    </DropdownMenuItem>
    <DropdownMenuItem
      className="text-destructive"
      data-cy="delete-action"
    >
      Delete
    </DropdownMenuItem>
  </DropdownMenuContent>
</DropdownMenu>

Toast Notifications

import { toast } from 'sonner'

// Success
toast.success('Task created successfully')

// Error
toast.error('Failed to create task')

// With action
toast('Task created', {
  action: {
    label: 'Undo',
    onClick: () => handleUndo(),
  },
})

Anti-Patterns

// NEVER: Modify core/components/ui/ directly
// Files in this directory are auto-generated by shadcn/ui

// CORRECT: Create extensions in theme
// contents/themes/{theme}/components/custom-button.tsx

// NEVER: Hardcode colors
className="bg-green-500 text-white border-gray-300"

// CORRECT: Use CSS variables
className="bg-success text-success-foreground border-input"

// NEVER: Skip forwardRef for inputs
function MyInput(props) {
  return <input {...props} />  // Can't attach refs!
}

// CORRECT: Use forwardRef
const MyInput = React.forwardRef((props, ref) => (
  <input ref={ref} {...props} />
))

// NEVER: Missing accessibility attributes
<button
  {isOpen ? 'Close' : 'Open'}
</button>

// CORRECT: Include ARIA attributes
<button
 
  aria-expanded={isOpen}
  aria-controls="panel-id"
>
  {isOpen ? 'Close' : 'Open'}
</button>

// NEVER: Skip data-cy on interactive elements
<Button

// CORRECT: Always include data-cy
<Button data-cy="submit-form-btn"

Checklist

Before finalizing UI with shadcn/ui:

• Uses CSS variable colors (not hardcoded)
• Includes data-cy on all interactive elements
• Uses cn() for class merging
• Implements proper form validation with Zod
• Includes ARIA attributes where needed
• Uses forwardRef for custom inputs
• Follows compound component patterns
• Extensions are in theme directory, not core
• Keyboard navigation works correctly
• Loading states use Skeleton components

Related Skills

• tailwind-theming - CSS variables and theming
• react-patterns - React best practices
• cypress-selectors - data-cy naming conventions
• accessibility - WCAG compliance