no-leaked-timeout

Rule category

Correctness.

What it does

Enforce that every setTimeout in a component or custom hook has a corresponding clearTimeout.

Why is this bad?

Scheduling a timeout within the setup function of useEffect without canceling it in the cleanup function can lead to unwanted setTimeout callback executions and may also result in using stale values captured by previous render’s effects after each subsequent re-render.

Examples

Failing

import React, { useEffect, useState } from 'react';
 
function Example() {
  const [count, setCount] = useState(0);
 
  useEffect(() => {
    const timeoutId = setTimeout(() => console.log(count), 1000);
    //                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    //                - A 'setTimeout' created in 'useEffect' must be cleared in the cleanup function.
  }, []);
 
  return null;
}

Passing

import React, { useEffect, useState } from 'react';
 
function Example() {
  const [count, setCount] = useState(0);
 
  useEffect(() => {
    const timeoutId = setTimeout(() => console.log(count), 1000);
    return () => clearTimeout(timeoutId);
  }, []);
 
  return null;
}