Button Toggle (ON/OFF)

Difficulty: Warm-up

Problem Statement

Render a button that toggles between ON and OFF on each click.

Live Demo

Try the running app below — this is the target behavior for the challenge.

Button Toggle (ON/OFF) — Live Demo

What Interviewers Expect

• Single boolean state drives label.
• No duplicated state for label and toggle value.
• Handler uses functional update.

Step-by-Step Implementation

Step 1 — Boolean state

Track toggle with one boolean.

const [on, setOn] = useState(false);

Step 2 — Derive label from state

Button text should come from state, not hardcoded toggling.

<button onClick={() => setOn((v) => !v)}>{on ? 'ON' : 'OFF'}</button>

Complete Implementation

Copy-paste ready single-file solution. Use this as your reference after attempting the challenge yourself, or paste it into CodeSandbox / StackBlitz to run locally.

App.jsx

import React, {useState} from 'react';

export default function App() {
  const [on, setOn] = useState(false);

  return (
    <button type="button" onClick={() => setOn((v) => !v)}>
      {on ? 'ON' : 'OFF'}
    </button>
  );
}

Final Checklist

• UI works for primary flow
• Edge cases handled (empty/disabled/loading where relevant)
• State updates are immutable
• Components are readable and reasonably split
• You can explain trade-offs out loud in an interview

Next Challenge

Continue to the next item in the sidebar when you're comfortable implementing this from scratch in 30–45 minutes.