Now, let's move to the the next topic:

🧠 Javascript Functions & Scope

❓ Why functions matter
- Avoid repeating code
- Make logic reusable
- Improve readability
- Easier debugging
Real use cases:
- Form validation
- Calculations
- API handling
- Button click logic

🔧 What is a function
A function is a block of code designed to perform a task.
Think of it as 👉 Input → Logic → Output

✍️ Function Declaration

function greet() {
  console.log("Hello World");
}

Call the function
greet();

📥 Functions with parameters

function greetUser(name) {
  console.log("Hello " + name);
}

greetUser("Deepak");
- name is a parameter
- "Deepak" is an argument

🔁 Function with return value

function add(a, b) {
  return a + b;
}
javascript
let result = add(5, 3);
console.log(result);

- return sends value back
- Function execution stops after return

⚡ Arrow Functions (Modern JS)
Shorter syntax
Commonly used in React and APIs

const multiply = (a, b) => {
  return a * b;
};

Single line shortcut
const square = x => x * x;

🧠 What is Scope
Scope defines where a variable can be accessed.
Types of scope you must know:
- Global scope
- Function scope
- Block scope

🌍 Global Scope

let city = "Delhi";
function showCity() {
  console.log(city);
}

- Accessible everywhere
- Overuse causes bugs

🏠 Function Scope

function test() {
  let msg = "Hello";
  console.log(msg);
}

- msg exists only inside function

🧱 Block Scope (let & const)

if (true) {
  let age = 25;
}

- age cannot be accessed outside
- let and const are block scoped
⚠️ var ignores block scope (avoid it)

🚫 Common Beginner Mistakes
- Forgetting return
- Using global variables everywhere
- Confusing parameters and arguments
- Using var

🧪 Mini Practice Task
- Create a function to calculate square of a number
- Create a function that checks if a number is positive
- Create an arrow function to add two numbers
- Test variable scope using let inside a block

✅ Mini Practice Task – Solution 🧠

🔢 1️⃣ Function to calculate square of a number

function square(num) {
  return num * num;
}

console.log(square(5));
✔️ Output → 25

➕ 2️⃣ Function to check if a number is positive

function isPositive(num) {
  if (num > 0) {
    return "Positive";
  } else {
    return "Not Positive";
  }
}
javascript
console.log(isPositive(10));
console.log(isPositive(-3));

✔️ Output
- Positive
- Not Positive

⚡ 3️⃣ Arrow function to add two numbers

const add = (a, b) => a + b;
console.log(add(4, 6));
✔️ Output → 10

🧱 4️⃣ Test variable scope using let inside a block

if (true) {
  let message = "Hello Scope";
  console.log(message);
}
// console.log(message); ❌ Error

✔️ message exists only inside the block

🧠 Key takeaways
- Functions make code reusable
- return sends output
- Arrow functions are concise
- let respects block scope

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