useThrottle stops updating after React 18 StrictMode effect replay

[stanza24]

Description

useThrottle stops publishing new values when used inside React 18 StrictMode.

During the StrictMode effect replay, the useUnmount cleanup clears the pending timeout but leaves timeout.current set to the ID of the cancelled timeout.

When the effects are mounted again, useThrottle assumes that a timeout is still active. Subsequent values are only written to nextValue.current, but the cancelled callback can no longer publish them or reset timeout.current.

As a result, the throttled value stops updating indefinitely.

Environment

• react-use: 17.6.1 (also reproducible with 17.6.0)
• react: 18.3.1
• react-dom: 18.3.1

Reproduction

import React, { StrictMode, useState } from 'react';
import { createRoot } from 'react-dom/client';
import { useThrottle } from 'react-use';

const App = () => {
  const [value, setValue] = useState(0);
  const throttledValue = useThrottle(value, 100);

  return (
    <>
      <button onClick={() => setValue((current) => current + 1)}>
        Increment
      </button>
      <div>Value: {value}</div>
      <div>Throttled value: {throttledValue}</div>
    </>
  );
};

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

Click Increment after the initial StrictMode effect replay.

Expected behavior

throttledValue is updated within the configured throttle interval.

Actual behavior

value changes, but throttledValue remains unchanged indefinitely.

Suggested fix

Reset the timeout ref and pending-value flag during cleanup:

useUnmount(() => {
  if (timeout.current) {
    clearTimeout(timeout.current);
  }

  timeout.current = undefined;
  hasNextValue.current = false;
});

This allows the remounted effect to create a new timeout instead of treating the cancelled timeout as active.

I can submit a pull request with the fix and a StrictMode regression test if this approach is acceptable.