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mediumMachine Coding

Build an OTP Input

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01

Understand the problem

Build an N-box OTP input with auto-advance, backspace and paste.

ReactPasteBackspace
02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

Study the solution

Solve in

An OTP (one-time-password) input is the row of single-character boxes you fill after a 2FA / SMS code is sent. It looks trivial, but a good implementation forces you to handle focus management, keyboard events, paste, and controlled inputs all at once.

The mental model (the part that matters)

The single

Solution ready — 2 min read

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04

React solution

Complete solutionRun Playground
import { useState } from 'react';
import OtpInput from './src/OtpInput';

export default function App() {
  const [code, setCode] = useState('');
  const [done, setDone] = useState(false);

  return (
    <div style={{ fontFamily: 'system-ui, sans-serif', padding: 32, textAlign: 'center' }}>
      <h2 style={{ marginBottom: 6 }}>Verify your number</h2>
      <p style={{ color: '#666', marginTop: 0, marginBottom: 20 }}>
        Enter the 6-digit code. Try typing, pasting "123456", and backspace.
      </p>
      <div style={{ display: 'inline-block' }}>
        <OtpInput length={6}
          onChange={(v) => { setCode(v); setDone(false); }}
          onComplete={(v) => { setCode(v); setDone(true); }} />
      </div>
      <p style={{ marginTop: 22, fontFamily: 'monospace', fontSize: 16 }}>
        value: {code || '(empty)'} {done ? 'OK' : ''}
      </p>
    </div>
  );
}
05

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