useEventListener Hook
ReactJS
Hard
8 views
Problem Description
Create a hook to attach an event listener safely.
Output Format
Render a React component.
Constraints
Use a ref for the handler and bind/unbind in an effect.
Official Solution
import React, { useEffect, useRef, useState } from 'react';
function useEventListener(target, type, handler) {
const saved = useRef(handler);
useEffect(() => {
saved.current = handler;
}, [handler]);
useEffect(() => {
if (!target) return;
function listener(e) {
saved.current(e);
}
target.addEventListener(type, listener);
return () => target.removeEventListener(type, listener);
}, [target, type]);
}
export default function App() {
const [keys, setKeys] = useState([]);
useEventListener(window, 'keydown', (e) => {
setKeys((prev) => [e.key, ...prev].slice(0, 8));
});
return (
<div style={{ padding: 16 }}>
<h2 style={{ marginTop: 0 }}>meetcode key log</h2>
<div style={{ color: '#555' }}>Last keys: {keys.join(', ') || 'Press something'}</div>
</div>
);
}
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