React Hooks are simple JavaScript functions that we can use to isolate the reusable part from a functional component. Hooks can be stateful and can manage side-effects. React provides a bunch of standard in-built hooks: useState : To manage states. Returns a stateful value and an updater function to update it.

Use State

useState is the ability to encapsulate local state in a functional component. React has two types of components, one is class components which are ES6 classes that extend from React and the other is functional components.

const [state, useState] = useState();

example

import { useState } from 'react';

function Example() {
    // Declare a new state variable, which we'll call "count"
    const [count, setCount] = useState(0);

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

Use Effect

The useEffect Hook allows you to perform side effects in your components. Some examples of side effects are: fetching data, directly updating the DOM, and timers. useEffect accepts two arguments. The second argument is optional. useEffect(<function>, <dependency>)

By using this Hook, you tell React that your component needs to do something after render. React will remember the function you passed (we’ll refer to it as our “effect”), and call it later after performing the DOM updates.

import React, { useState, useEffect } from 'react';
function Example() {
  const [count, setCount] = useState(0);

  // Similar to componentDidMount and componentDidUpdate:  useEffect(() => {    // Update the document title using the browser API    document.title = `You clicked ${count} times`;  });
  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

Placing useEffect inside the component lets us access the count state variable (or any props) right from the effect. We don’t need a special API to read it — it’s already in the function scope. Hooks embrace JavaScript closures and avoid introducing React-specific APIs where JavaScript already provides a solution.