React – Component Rules

Rule	Correct	Incorrect
Component type	Functional + hooks	Class components
File name	UserCard.jsx (PascalCase)	userCard.js
One per file	One component per file	Multiple exports
Component size	< 200 lines	> 300 lines — break it up
Default export	export default UserCard	Anonymous default exports

Correct Example

const UserCard = ({ userId, onClose }) => {
  return <div>{userId}</div>;
};

export default UserCard;

Incorrect Example

export default ({ userId, onClose }) => {
  return <div>{userId}</div>;
};