Functions

Learn how to create reusable blocks of code and organize JavaScript programs using functions.

What is a Function?

A function is a reusable block of code that performs a specific task.

When the same task is required multiple times in a program, we can place that logic inside a function and call the function whenever needed.

This makes the program easier to organize and reduces repeated code.

Why Do We Use Functions?

Reusability

Write a task once and call the same function whenever you need it.

Organization

Divide a large program into smaller, meaningful blocks of code.

Maintainability

Keep related logic together so it is easier to update and understand.

Basic Function Syntax

function functionName() {
    // code to execute
}

functionName();

Understanding the Syntax

function is the keyword used to create a function.

functionName is the name given to the function.

Parentheses () are used for parameters. They can be empty.

Curly braces { } contain the statements that execute when the function runs.

functionName() calls the function and executes its code.

How a Function Works

Define Function → Call Function → Execute Code → Result

Define Function Create reusable code

→

Call Function functionName()

→

Execute Code Run the function body

→

Result Output or returned value

Example 1: Creating and Calling a Function

In this example, we create a function named showWelcome.

The code inside the function runs when we call showWelcome().

function showWelcome() {
    console.log("Welcome to CIIT Training Institute!");
    console.log("Start learning JavaScript.");
}

showWelcome();

Output

Welcome to CIIT Training Institute!
Start learning JavaScript.

Example 2: Function with a Parameter

A function can accept information through parameters. A parameter works like a variable inside the function.

Here, studentName receives the value "Gauri" when the function is called.

function greetStudent(studentName) {
    console.log("Hello, " + studentName);
    console.log("Welcome to JavaScript!");
}

greetStudent("Gauri");

Output

Hello, Gauri
Welcome to JavaScript!

Important Note

Function Definition vs Function Call

Defining a function creates the reusable block of code.

Calling the function executes the statements inside that function.

Function Topics

Function Declaration

Learn how to declare and call traditional JavaScript functions.

Parameters & Arguments

Learn how functions receive input values.

Return Values

Learn how a function can return a result.

Arrow Functions

Learn the shorter syntax for writing functions.

Callback Functions

Learn how functions can be passed to other functions.

Summary

A function is a reusable block of JavaScript code designed to perform a specific task. Functions help reduce repeated code and make programs easier to organize and maintain. A function can be called whenever its task is required and can also receive parameters or return values.