JAVASCRIPT

useEffect react dependency

function EffectsDemoTwoStatesWithDependeny() {
  const [title, setTitle] = useState("default title");
  const titleRef = useRef();
  const [darkMode, setDarkMode] = useState(false);
  useEffect(() => {
    console.log("useEffect");
    document.title = title;
  }, [title]);
  console.log("render");
  const handleClick = () => setTitle(titleRef.current.value);
  const handleCheckboxChange = () => setDarkMode((prev) => !prev);
  return (
    <div className={darkMode ? "view dark-mode" : "view"}>
      <label htmlFor="darkMode">dark mode</label>
      <input
        name="darkMode"
        type="checkbox"
        checked={darkMode}
        onChange={handleCheckboxChange}
      />
      <input ref={titleRef} />
      <button onClick={handleClick}>change title</button>
    </div>
  );
}

dependency list useeffect

import { useEffect } from 'react';
function MyComponent() {
  useEffect(() => {
    // Runs ONCE after initial rendering
  }, []);
}

dependency list useeffect

import { useEffect, useState } from 'react';
function MyComponent({ prop }) {
  const [state, setState] = useState('');
  useEffect(() => {
    // Runs ONCE after initial rendering
    // and after every rendering ONLY IF `prop` or `state` changes
  }, [prop, state]);
}