useCallback Stable Handler

useCallback Stable Handler

Hard ReactJS Performance & Patterns 26 views
Explanation Complexity

Problem Statement

Use useCallback to keep a stable function reference for a memoized child.

Input Format

No input.

Output Format

Render a React component.

Constraints

Wrap handler in useCallback and memoize child component.

Input / Output Format

Input Format
No input.
Output Format
Render a React component.
Constraints
Wrap handler in useCallback and memoize child component.

Examples

Input:
Output:
(React code)

Example Solution (Public)

ReactJS 
import React, { useCallback, useState } from 'react';

const Child = React.memo(function Child({ onPing }) {
  return (
    <button type='button' onClick={onPing} style={{ padding: '10px 14px', borderRadius: 12, border: '1px solid #ddd', background: '#fff' }}>
      Ping
    </button>
  );
});

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

  const onPing = useCallback(() => setPings((n) => n + 1), []);

  return (
    <div style={{ padding: 16 }}>
      <h2 style={{ marginTop: 0 }}>meetcode callbacks</h2>
      <Child onPing={onPing} />
      <div style={{ marginTop: 10, color: '#555' }}>Pings: {pings}</div>
      <button type='button' onClick={() => setCount((n) => n + 1)} style={{ marginTop: 12, padding: '8px 12px', borderRadius: 12, border: 0, background: '#0b5', color: '#fff' }}>Unrelated state ({count})</button>
    </div>
  );
}

Official Solution Code

import React, { useCallback, useState } from 'react';

const Child = React.memo(function Child({ onPing }) {
  return (
    <button type='button' onClick={onPing} style={{ padding: '10px 14px', borderRadius: 12, border: '1px solid #ddd', background: '#fff' }}>
      Ping
    </button>
  );
});

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

  const onPing = useCallback(() => setPings((n) => n + 1), []);

  return (
    <div style={{ padding: 16 }}>
      <h2 style={{ marginTop: 0 }}>meetcode callbacks</h2>
      <Child onPing={onPing} />
      <div style={{ marginTop: 10, color: '#555' }}>Pings: {pings}</div>
      <button type='button' onClick={() => setCount((n) => n + 1)} style={{ marginTop: 12, padding: '8px 12px', borderRadius: 12, border: 0, background: '#0b5', color: '#fff' }}>Unrelated state ({count})</button>
    </div>
  );
}
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