🌟 Functions & If-Else in JavaScript: Beginner’s Guide

Functions are the building blocks of JavaScript. They let us reuse code, make our programs cleaner, and reduce repetition. In this guide, we’ll explore functions, return values, and decision-making with if-else using simple examples.

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🔹 What is a Function?

A function is a block of code designed to perform a particular task.

👉 You define a function once and can reuse it whenever needed.

✅ Function Syntax

function functionName(parameters) {
    // code to be executed
}

• functionName → Name of the function (e.g., greet, sum)

• parameters → Input values (like variables)

• return → Used to send output back from the function

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1️⃣ Function Declaration & Invocation

Example: Printing "Hello World"

function printHelloworld() {
    console.log("Hello World");
}
printHelloworld(); // Function call

👉 A function must be invoked (called) to run its code.

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2️⃣ Passing Arguments to Functions

Functions can take inputs (parameters).

Example: Greeting Someone

function greet(name) {
    console.log("Namaste, " + name);
}

greet("Virat Kohli");
greet("Kamlesh");

📝 Output:

Namaste, Virat Kohli
Namaste, Kamlesh

💡 Functions become more dynamic when we pass values.

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3️⃣ Functions with Calculations

Let’s create functions that add and multiply numbers.

function sum(a, b) {
    let add = a + b;
    console.log(add);
}

sum(1, 3);  // Output: 4
sum(2, 3);  // Output: 5

function multiply(a, b) {
    let multiple = a * b;
    console.log(multiple);
}

multiply(3, 2);  // Output: 6

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4️⃣ Returning Values from Functions

Instead of just printing, functions can return values for later use.

function square(x) {
    let result = x * x;
    return result;
}

let value = square(3);
console.log(value); // Output: 9

💡 Difference:

• console.log() → Just displays result

• return → Sends result back to be stored or reused

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🧩 Decision Making with If-Else

Programs often need to make choices. In JavaScript, we use if-else statements for decision-making.

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Example 1: Voting Eligibility

function eligibleToVote(age) {
    if (age < 1) {
        console.log("Invalid Input");
    } else if (age < 18) {
        console.log("Not Eligible");
    } else {
        console.log("Eligible to Vote");
    }
}

eligibleToVote(0);   // Invalid Input
eligibleToVote(15);  // Not Eligible
eligibleToVote(18);  // Eligible to Vote

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Example 2: Even or Odd Check

function isEvenOdd(n) {
    if (n % 2 == 0) {
        console.log("Number is Even");
    } else {
        console.log("Number is Odd");
    }
}

isEvenOdd(16); // Output: Number is Even
isEvenOdd(7);  // Output: Number is Odd

💡 % is the modulus operator → gives remainder after division.

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⚡ Quick Recap

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🎯 Key Takeaways

• Functions help in code reusability.

• return makes functions more powerful than just logging.

• if-else allows decision making in programs.

• Always test your function with different inputs.

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✨ With this knowledge, you can now start writing reusable, dynamic, and interactive programs in JavaScript!

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