Business
Jobs
  • About Us
  • Solutions
    • Job Postings
      Post your job and receive qualified candidates in 48h.
    • Candidate Assessments
      500+ technical and psychological tests, plus anti-fraud.
    • Headhunting
      Tailor-made executive search from start to finish.
    • Payroll + EOR
      Payroll dispersal and EOR across 15+ LATAM countries.
  • Pricing
  • Jobs

0

217
Views
how to execute cleanup function in useEffect() only when component unmounts

I want to clear filters only when the component unmounts. So I wrote cleanup function only in useEffect(). But as I checked it with console.log(), 1 was printed after the component mounted too. What's wrong in this way?

useEffect(() => {
  return () => {
    clearFilters();
    console.log(1);
  };
}, []);

Stack Snippet:

const { useState, useEffect } = React;

const Example = () => {
    useEffect(() => {
        return () => {
            // clearFilters();
            console.log(1);
        };
    }, []);
    return <div>x</div>;
};

const App = () => {
    const [showExample, setShowExample] = useState(false);
    
    return <div>
        <label>
            <input type="checkbox" checked={showExample} onChange={({currentTarget: {checked}}) => setShowExample(checked)} />
            Show <code>Example</code> component
        </label>
        <div>
            {showExample ? <Example /> : null}
        </div>
    </div>;
};

const root = ReactDOM.createRoot(document.getElementById("root"));
root.render(<App />);
<div id="root"></div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/18.1.0/umd/react.development.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/18.1.0/umd/react-dom.development.js"></script>

Here's a more detailed code below

import React, { useEffect } from 'react';
import { useFilterContext } from 'contexts/FilterContext';
import classNames from 'classnames/bind';
import Rating from 'components/Rating/Rating';
import { Button, Form } from 'react-bootstrap';
import styles from './Filter.module.scss';

const cn = classNames.bind(styles);

const Filter = () => {
  const {
    filters: { byAscendingPrice, byStock, byFastDelivery, rating },
    dispatch,
  } = useFilterContext();

  const clearFilters = () => dispatch({ type: 'CLEAR_FILTERS' });
  useEffect(() => {
    return () => clearFilters();
  }, []);

  return (
     // Some components
  );
};

export default Filter;
about 4 years ago · Juan Pablo Isaza
2 answers
Answer question

0

You might be using React's strict mode which simulates unmounting and remounting a component when a component is mounted. This causes double renders in development.

about 4 years ago · Juan Pablo Isaza Report

0

This is because of the strict mode. In Strict mode, react may invoke render phase lifecycles multiple times. So it prints 1 on the mounting of the component. But the interesting thing to note here is that it only happens in Development mode, not in Production mode.

Here's the link to read more about React's strict mode: Link

about 4 years ago · Juan Pablo Isaza Report
Answer question
Find remote jobs

Discover the new way to find a job!

Top jobs
Top job categories
Business
Post vacancy Pricing Sales
Legal
Terms and conditions Privacy policy
© 2026 PeakU Inc. All Rights Reserved.
Andres GPT
Show me some job opportunities
There's an error!