PropTypes in React — React Technical Interview Questions & Answers

PropTypes in React

PropTypes in React

  • PropTypes is a runtime checker you attach to a function or class: MyComp.propTypes = { … }. isRequired marks must-have props. defaultProps (or default parameters) fill gaps. You import from 'prop-types', not from 'react' (that split happened years ago).
  • If the team already uses TypeScript, don’t add PropTypes ‘for extra safety’ on every file — you’ll maintain two sources of truth. Pick one.
  • PropTypes in React — on screen: Pen × 1. Missing qty uses default. Wrong type → dev warning.

Technical Interview Tip: prop-types package + isRequired. TS in new code.

Code Examples for PropTypes in React

Example

// PropTypes + default
import PropTypes from "prop-types";

function Item({ title, qty }) {
  return <li>{title} × {qty}</li>;
}

Item.propTypes = {
  title: PropTypes.string.isRequired,
  qty: PropTypes.number,
};
Item.defaultProps = { qty: 1 };

PropTypes in React — on screen: Pen × 1. Missing qty uses default. Wrong type → dev warning.

How to Explain PropTypes in React to an Interviewer

Explain PropTypes as if you are teaching a junior — definition, then one tiny UI.

Runtime prop checks (dev). prop-types.

What does the example show on screen (or print), and what does that prove?

PropTypes in React — on screen: Pen × 1

What mistake do freshers make with PropTypes?

TS usually replaces it.