useeffect first render code example

Example 1: react useeffect not on first render

//This is a way to build this effect as a custom hook
import React, { useEffect, useRef } from 'react';

const useDidMountEffect = (func, deps) => {
    const didMount = useRef(false);

    useEffect(() => {
        if (didMount.current) func();
        else didMount.current = true;
    }, deps);
}

export default useDidMountEffect;

Example 2: useEffect

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>
  );
}

Example 3: useeffect on update

const isInitialMount = useRef(true);

useEffect(() => {
  if (isInitialMount.current) {
     isInitialMount.current = false;
  } else {
      // Your useEffect code here to be run on update
  }
});