useing the {React.memo} with out {useCallback}

Question

In the code below, even if {useCallback} is not used for the {countUp} and {countDown} functions, from the {React.memo} point of view in the {AppTwo} component receiving the two functions as props, even though the two functions are newly created, the old Since it is equal to the value of , isn't it possible to prevent re-rendering? Why is it re-rendering?

function App(){

  const [count,setCount]=useState(0);

  function countUp(){
    setCount(count=>count+1);
  }
  function countDown(){
    setCount(count=>count-1);
  }

  return(
    <div>
      <p>count:{count}</p>
      <AppTwo countUp={countUp} countDown={countDown}/>
    </div>
  )  
}

const AppTwo=React.memo(

  ({countUp, countDown})=>{

  useEffect(()=>{
    console.log('re-rendering.')
  })

  return(
    <div>
      <button onClick={countUp}>count UP</button>
      <button onClick={countDown}>count DOWN</button>
    </div>
  )
})

Answer 1

By providing an empty dependency array to useEffect in AppTwo, you ensure that the effect is only run once, effectively avoiding unnecessary re-renders caused by the effect itself.

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

export function App() {
  const [count, setCount] = useState(0);

  function countUp() {
    setCount(prevCount => prevCount + 1);
  }

  function countDown() {
    setCount(prevCount => prevCount - 1);
  }

  return (
    <div>
      <p>count: {count}</p>
      <AppTwo countUp={countUp} countDown={countDown} />
    </div>
  );
}

const AppTwo = React.memo(({ countUp, countDown }) => {
  useEffect(() => {
    console.log('re-rendering.');
  },[]); ///  add  this will  be  fix  your  issuie

  return (
    <div>
      <button onClick={countUp}>count UP</button>
      <button onClick={countDown}>count DOWN</button>
    </div>
  );
});