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JavaScript Function

Last Updated on July 28, 2023 by Mayank Dham

JavaScript Functions are blocks of code designed to perform specific tasks. They enable you to break down complex problems into smaller, manageable chunks, making your code more organized, reusable, and easier to understand. JavaScript provides a wide range of built-in functions, such as Math.sqrt(), for various computations. However, you can also create your own custom functions to extend the functionality of your programs.

Declaring a JavaScript Function

To declare a function in JavaScript, you use the function keyword, followed by the name of the function and parentheses containing optional parameters. The function’s code block is enclosed within curly braces {}.

// Declaring a function named greet()
function greet() {
    console.log("Hello there");

JavaScript Call Function

Once you’ve declared a function, you can call it by using its name followed by parentheses.

// Function call

greet(); // calling a function

JavaScript Function Parameters

Functions can also accept parameters, which are values passed to the function when it is declared. These parameters act as placeholders for the values that will be used in the function’s calculations.

// Function with a parameter
function greet(name) {
    console.log("Hello " + name + ":)");

// Calling the function with an argument


Hello Simon :)

JavaScript Function Example

Here’s an example of a function that adds two numbers:

// Function to add two numbers
function add(a, b) {
    console.log(a + b);

// Calling the function with different arguments
add(3, 4);
add(2, 9);



Return Statement in JavaScript Function

The return statement is used to return a value from a function. It also indicates the end of the function’s execution. If no value is explicitly returned, the function returns undefined.

function add(a, b) {
    return a + b;

let result = add(3.4, 4);
console.log("The sum is " + result);


The sum is 7.4

Advantages of Using JavaScript Functions

Functions offer several advantages in JavaScript programming:

1. Reusability: You can declare a function once and use it multiple times throughout your code, reducing redundancy and promoting code reusability.

2. Readability: Dividing your code into functions makes it easier to understand, as each function is dedicated to a specific task.

3. Organization: Functions help organize your code into smaller logical units, making it easier to maintain and debug.

JavaScript Function Expressions

In JavaScript, you can define functions using expressions, where the function is assigned to a variable. These are called function expressions or anonymous functions.

let square = function(num) {
    return num * num;




Function expressions allow you to create functions on the fly and assign them to variables, making them versatile and flexible in various programming scenarios.

Functions are an essential part of JavaScript programming. They empower you to break down complex problems, improve code reusability, and create more organized and readable code. Additionally, function expressions provide added flexibility to create functions dynamically. Understanding functions and their practical applications will significantly enhance your JavaScript programming skills.

Frequently Asked Questions (FAQs)

Here are some of the frequently asked questions about JS functions

Q1: What is a function in JavaScript?
In JavaScript, a function is a block of code that performs a specific task or set of tasks. It is a reusable and self-contained unit of code that can be called multiple times throughout a program. Functions are used to divide a complex problem into smaller, manageable parts, making code organization and maintenance easier. They play a fundamental role in JavaScript programming and are essential for building modular and efficient applications.

Q2: What are the 3 types of functions in JavaScript?
In JavaScript, there are three types of functions:

1. Named Functions: These are traditional functions declared with a function name followed by parentheses and a function body enclosed in curly braces.

2. Anonymous Functions: These functions do not have a name and are usually defined within expressions or as arguments to other functions. They are commonly used as callbacks in asynchronous operations.

3. Arrow Functions: Introduced in ES6, arrow functions provide a more concise syntax for writing functions. They are commonly used for short, single-expression functions.

Q3: What are function types in JavaScript?

In JavaScript, functions can be categorized into the following types based on their usage:

1. Regular Functions: These are typical named functions or anonymous functions that are used to perform specific tasks and can be called using their names.

2. Higher-Order Functions: Higher-order functions are functions that accept other functions as arguments or return functions as their results. They are powerful tools for functional programming and provide a way to abstract over actions, behaviors, or computations.

3. Immediately Invoked Function Expressions (IIFE): An IIFE is a function that is declared and executed immediately after it is defined. It is commonly used to create a private scope and avoid polluting the global namespace.

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