What is the useEffect hook and when do you use it? - React Interview Questions | React Developer Jobs & Interview Prep

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What is the useEffect hook and when do you use it?

Hooks

#useEffect#side-effects#lifecycle#data-fetching

Answer

useEffect is a React hook that lets you perform side effects in function components.

It runs after every render and can be used for data fetching, subscriptions, or manually changing the DOM.

useEffect replaces componentDidMount, componentDidUpdate, and componentWillUnmount from class components.

It's essential for handling side effects in function components.

import React, { useState, useEffect } from 'react';

function Example() { const [data, setData] = useState(null);

useEffect(() => { // Fetch data when component mounts fetch('/api/data') .then(response => response.json()) .then(data => setData(data));

}, []); // Empty dependency array = run only on mount

return <div>{data ? data.title : 'Loading...'}</div>; }