Careeroza

React 17+

What Changed

Modern browsers do not need pooling, and it confused developers, so React 17 removed event pooling. Events can be read anywhere, any time. e.persist() still exists but does nothing.

Example

In React 17+ (this preview uses React 18) reading the event inside a timeout works.

export default function App() {
  const handleChange = (e) => {
    setTimeout(() => console.log('value later:', e.target.value), 500);
  };
  return <input placeholder="Type something" onChange={handleChange} />;
}

Result

Event Delegation Change

	React 16	React 17+
Event pooling	yes (needs e.persist())	no
Listeners attached to	document	the root container (#root)
Effect	multiple React versions on a page conflicted	safe to embed several React apps

Note: React never adds a listener to every button: it uses event delegation, one listener per event type at the root, and dispatches to your handlers.