import React, { useState }from 'react'


    const App = () => {


  const [myName, setMyName] = useState("Parveen Barak");

  const changeName = () => {

    let val = myName;

    if (val==="Parveen Barak"){
      setMyName("Deepak Kumar")
    }else{
      setMyName("Parveen Barak");
    }
    
  }

  console.log(myName);
  return (
    <div>
      <h1>{ myName }</h1>
      <button className="btn" onClick={changeName}>Click me</button>
      
    </div>
  )
}

export default App


--------------------------------------------------------------------------------------------------------------------------------------------------------------

Example - 2 

import React, { 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>
  );
}