Conditional Classes in React — React Technical Interview Questions & Answers

Conditional Classes in React

Conditional Classes in React

  • Same problem, class-list angle. A tiny cx helper: parts.filter(Boolean).join(' ') turns ('tab', on && 'tab-on') into 'tab tab-on' or 'tab'. That’s what clsx does. Use it when you have three flags (disabled, active, error).
  • Conditional Classes in React — output: "tab tab-on" then "tab". Libraries like clsx do this.

Technical Interview Tip: cx / clsx for several flags.

Code Examples for Conditional Classes in React

Example

// Conditional classes
function cx(...parts) {
  return parts.filter(Boolean).join(" ");
}

export default function Tab({ on }) {
  return <button className={cx("tab", on && "tab-on")}>Home</button>;
}

Conditional Classes in React — output: "tab tab-on" then "tab". Libraries like clsx do this.

How to Explain Conditional Classes in React to an Interviewer

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

Helper : filter(Boolean).join. Lib : clsx.

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

Conditional Classes in React — output: "tab tab-on" then "tab"

What mistake do freshers make with Conditional Classes?

Flags : disabled / active / error.