Function Declaration

Learn how to declare a JavaScript function, understand its parts, and call it to execute reusable code.

What is a Function Declaration?

A function declaration is a standard way of defining a named function in JavaScript.

The declaration specifies the function name, optional parameters, and the block of code that should execute when the function is called.

Once declared, the same function can be called multiple times whenever the task is required.

A JavaScript function declaration creates a reusable block of code.

Basic Structure

function functionName(parameter1, parameter2) {
    // function body
}

functionName(value1, value2);

Parts of a Function Declaration

function Keyword

The function keyword tells JavaScript that we are declaring a function.

Function Name

The function name identifies the function and is used when calling it.

Function Body

The statements inside curly braces form the function body.

How Function Declaration Works

Declare → Call → Execute

Declare Function function greet() { }

→

Call Function greet()

→

Execute Body Run statements

→

Output Display result

Example 1: Simple Function Declaration

Here, the greetStudent function is declared with a name and a simple function body.

The function is executed by calling greetStudent().

function greetStudent() {
    console.log("Welcome to JavaScript!");
    console.log("Start practicing functions.");
}

greetStudent();

Output

Welcome to JavaScript!
Start practicing functions.

Example 2: Calling a Function Multiple Times

One important benefit of a function is reusability. After declaring a function once, we can call it multiple times.

function showCourse() {
    console.log("JavaScript Full Stack");
}

showCourse();
showCourse();
showCourse();

Output

JavaScript Full Stack
JavaScript Full Stack
JavaScript Full Stack

Important Note

Function Name Should Be Meaningful

Use a clear function name that describes the task performed by the function.

Names such as calculateTotal(), showCourse(), and greetStudent() make code easier to understand.

Summary

A function declaration uses the function keyword followed by a function name, parentheses, and a function body. The declared function can then be called whenever its task is required. Function declarations are useful for creating reusable and organized JavaScript code.