useEffect hook Simple and accurate explanation

React has one job:
👉 Take data → show UI

But real apps need more than just showing UI. You also need to:

• fetch data from APIs
• set timers
• store data
• listen to events

These things are outside React’s job.

So useEffect lets you run code after React updates the screen, especially for things outside React.

👉 React renders UI
👉 Then useEffect runs side work

⚠️ The part most people miss (important)

useEffect is not just “run after render”

It’s: “Run after render — but only when something changes (if you tell it what to watch)”

The 3 real behaviors (this is where clarity comes)

1.Run every time (default)

useEffect(() => {
  console.log("Runs after every render");
});

👉 No control → runs again and again
👉 Usually a bad idea

2.Run only once (on mount)

useEffect(() => {
  console.log("Runs only once");
}, []);

👉 Like: “Do this when the page loads”

3.Run when something changes (MOST IMPORTANT)

useEffect(() => {
  console.log("Runs when count changes");
}, [count]);

👉 “Only run when count changes”