React useState and useEffect Hooks – Explanation with Examples
React.js
React useState and useEffect Hooks – Explanation with Examples
React Hooks make functional components more powerful and easier to manage. Among all hooks, useState and useEffect are the most commonly used. In this article, you will learn why they are used, how they work, and where to use them with simple examples.
Quick Summary
- useState is used to store and update data inside a component.
- useEffect is used to run side effects such as API calls, timers, and DOM updates.
- Both hooks are essential for building dynamic React applications.
What is useState in React?
The useState hook is used to manage state inside a functional component. State means data that can change over time.
Why use useState?
- To store dynamic values inside a component
- To update UI automatically when values change
- To manage counters, forms, and toggles
- To make functional components interactive
Syntax of useState
const [state, setState] = useState(initialValue);
state → Current value
setState → Function used to update value
initialValue → Default starting value
Example of useState
Below example shows a simple counter using useState.
import React, { useState } from "react";
function Counter() {
const [count, setCount] = useState(0);
return (
<div>
<h2>Counter: {count}</h2>
<button onClick={() => setCount(count + 1)}>
Increase
</button>
</div>
);
}
export default Counter;
Explanation
Here count stores the current value and setCount updates it. When the button is clicked, React re-renders the component.
What is useEffect in React?
The useEffect hook is used to perform side effects in a component.
Why use useEffect?
- Fetching API data
- Running code on component load
- Managing timers and intervals
- Updating DOM
Syntax of useEffect
useEffect(() => {
// side effect code
}, [dependency]);
[] → Runs once when component loads
[value] → Runs when value changes
No dependency → Runs after every render
Conclusion
Both useState and useEffect are essential React hooks. useState manages data, while useEffect handles side effects like API calls.
Frequently Asked Questions
Why use useState in React?
It stores and updates dynamic data inside components.
Why use useEffect?
To perform side effects such as API calls and timers.
Can both hooks be used together?
Yes, usually useEffect fetches data and useState stores it.
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