Component Interface

Problem

Components become fragile black boxes where it’s unclear what properties are required, what types they expect, or what they return. Changes to one component silently break others, and bugs only surface at runtime when users encounter “undefined is not a function” or receive malformed data.

Solution

Use TypeScript interfaces or PropTypes to explicitly declare what props a component accepts, their types, and which are required. This catches mismatches at compile time and provides inline documentation that makes components self-describing.

Example

This example demonstrates how to define a TypeScript interface for component props that specifies required and optional properties with their types.

// Define the contract for Button component props
interface ButtonProps {
  label: string;                         // Required: button text
  onClick: () => void;                   // Required: click handler function
  disabled?: boolean;                    // Optional: disabled state
  variant?: 'primary' | 'secondary';     // Optional: style variant with allowed values
}

// Component uses the interface to enforce the contract and provide default values
function Button({ label, onClick, disabled, variant = 'primary' }: ButtonProps) {
  return <button onClick={onClick} disabled={disabled}>{label}</button>;
}

Benefits

• Catches prop type mismatches at compile time before runtime errors occur.
• Provides inline documentation that makes components self-describing.
• Enables better IDE autocomplete and inline help.
• Makes refactoring safer by catching all places that need updates.
• Documents required vs optional props without reading implementation.

Tradeoffs

• Adds type definition overhead for every component.
• Can become verbose for components with many props or complex types.
• PropTypes add runtime overhead unlike TypeScript compile-time checks.
• Requires learning TypeScript or PropTypes syntax for the team.
• May need to maintain separate types for internal implementation details.