useEffect hook Simple and accurate explanation

Aanand — Mon, 27 Apr 2026 12:08:10 +0000

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”

How your compiler finds the data that is stored inside the variable (Symbol table)

Aanand — Mon, 27 Oct 2025 05:18:59 +0000

Have you ever typed print(variable_name) and wondered how your compiler actually finds the data by using variable name? It's like magic, but there's a fascinating process working behind the scenes!

Variables are like house Addresses
Think of computer memory like a giant apartment building with millions of rooms. Each room has a number address like "Room #0x1000.

when you write:

int num = 37;

Here's what happens:

Find an empty room: The compiler finds an available memory location (say, room #0x1000)
Move in the value: The number 37 moves into this room.
Put up a name tag: The variable name "num" becomes the friendly name for this address.

The Compiler's Secret Address Book
So when your program actually runs, all those name tags disappear! how does
cout << num still work?
The compiler keeps a secret address book called a symbol table:

┌────────────┬──────────────────┐
│ Variable   │ Memory Address   │
├────────────┼──────────────────┤
│ num        │ 0x1000           │
│ age        │ 0x1004           │
│ name       │ 0x2000           │
└────────────┴──────────────────┘

When you print a variable:

cout << num;

The compiler:

Looks up "num" in its address book
Finds it lives at memory address 0x1000
Sends instructions: "Go to address 0x1000 and print what's inside!"

Variable names are for humans — memory addresses are for compiler!

DEV Community: Aanand

useEffect hook Simple and accurate explanation

⚠️ The part most people miss (important)

How your compiler finds the data that is stored inside the variable (Symbol table)