Build a React Counter Component with useState

easy

By FrontendAtlas Editorial · Updated Aug 20, 2026

easy level

React useState Event handlers Derived disabled state

Build a React counter component with the useState hook. Initialize the count at zero, wire increment and guarded decrement handlers, disable decrement at zero, and keep the rendered value synchronized with state.

React useState

Event handlers

Derived disabled state

Requirements

Render a <Counter /> as the main UI.
Display the current count value.
Provide '+' and '-' buttons to increment and decrement.
Prevent the count from ever going below 0.

Expected behavior

Clicking '+' increases the count by 1.
Clicking '-' decreases the count by 1, but never below 0.
Initial count starts at 0.

Implementation notes

Initialize local component state with useState(0).
Guard the decrement so it never sets a negative value.
Disable decrement at zero so the interface communicates the invariant.
Keep everything in a single small component for this exercise.

FAQ

How do you build a counter component in React with useState?

Call useState(0) to store the count, render that state, and update it from increment and decrement button handlers. Guard decrement so the value cannot fall below zero.

How do you prevent a React counter from going below zero?

Guard the decrement so it clamps at zero, then disable the decrement button when count is zero to keep behavior and visual state aligned.

Solution

Overview

A single count state drives the UI. Increment adds 1, decrement subtracts 1 but clamps at 0. Disabling the minus button at zero communicates the rule to users and prevents invalid negative values. This is a clean example of state-driven UI and controlled updates. Performance & pitfalls: consider edge cases (empty state, rapid clicks), trade-offs in state shape, and accessibility of interactive controls.

Single component with guarded decrement

Initialize count with useState(0). Implement inc as setCount(c => c + 1) and dec as setCount(c => Math.max(0, c - 1)). Bind the decrement button’s disabled prop when count === 0, and render the count in the UI so every click immediately reflects the new state. Edge cases & testing: cover invalid inputs, ensure predictable reactivity, and keep the UI stable under rapid updates.

Files

{
  "name": "react-counter",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "react": "18.x",
    "react-dom": "18.x",
    "react-scripts": "5.0.1"
  },
  "scripts": { "start": "react-scripts start" }
}

{
  "compilerOptions": {
    "jsx": "react-jsx",
    "target": "ES2020",
    "module": "ESNext",
    "strict": true
  }
}

<!doctype html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><title>React SDK • Counter</title></head><body><div id="root"></div></body></html>

:root {
  color-scheme: dark;
}

html, body {
  margin: 0;
  height: 100%;
  background: #0a0a0a;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
}

.main {
  min-height: 100vh;
  background: #0a0a0a;
  color: #e5e7eb;
  display: grid;
  place-items: center;
  padding: 24px;
}

.section {
  width: 100%;
  max-width: 420px;
  display: grid;
  gap: 16px;
}

h1 {
  margin: 0;
  font-size: 20px;
  font-weight: 700;
}

.panel {
  background: #0b1020;
  border: 1px solid #1f2937;
  border-radius: 12px;
  padding: 16px;
}

.value {
  font-size: 48px;
  font-weight: 800;
  text-align: center;
  margin-bottom: 12px;
}

.actions {
  display: flex;
  gap: 8px;
  justify-content: center;
}

button {
  background: #a3e635;
  color: #111;
  border: none;
  border-radius: 10px;
  padding: 10px 14px;
  font-weight: 700;
  cursor: pointer;
}

button[disabled] {
  opacity: .5;
  cursor: not-allowed;
}

button.ghost {
  background: transparent;
  color: #e5e7eb;
  border: 1px solid #374151;
}

import React, { useState } from 'react';
import './App.css';

export default function App() {
  const [count, setCount] = useState(0);
  const isZero = count === 0;

  const inc = () => {
    setCount((c) => c + 1);
  };

  const dec = () => {
    setCount((c) => (c > 0 ? c - 1 : 0));
  };

  const reset = () => {
    setCount(0);
  };

  return (
    <main className="main">
      <section className="section">
        <h1>Counter</h1>

        <div className="panel">
          <div className="value">{count}</div>

          <div className="actions">
            <button onClick={dec} disabled={isZero}>−</button>
            <button onClick={inc}>+</button>
            <button onClick={reset} className="ghost">Reset</button>
          </div>
        </div>
      </section>
    </main>
  );
}

import React from 'react';
import { createRoot } from 'react-dom/client';
import App from './App';

createRoot(document.getElementById('root')!).render(<App />);

Notes & Pitfalls

Pitfalls

Updating the value without clamping, which allows negatives.
Recomputing from stale state instead of using the current value correctly.

Techniques

Using `useState` for local component state.
Guarding updates with `Math.max`.

Guides

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