How to Use JavaScript Functions - Practical Examples

Functions are a fundamental part of JavaScript that allow you to encapsulate reusable code. In this guide, we'll explore how to use JavaScript functions with practical examples to demonstrate their usage.

Defining a Function

To define a function in JavaScript, use the function keyword, followed by a name and a pair of parentheses for parameters. Here's an example:

function greet(name) {
console.log("Hello, " + name + "!");

Calling a Function

To call a function, use its name followed by parentheses, passing any required arguments:

greet("John"); // Calling the greet function with an argument

Function with Return Value

Functions can return values using the return statement. Here's an example of a function that returns the sum of two numbers:

function add(a, b) {
return a + b;
const result = add(5, 3); // Calling the function and storing the result

Function with Default Parameters

You can set default values for function parameters. If an argument is not provided, the default value is used:

function greet(name = "Guest") {
console.log("Hello, " + name + "!");
greet(); // No argument, uses the default value
greet("Alice"); // Provides an argument

Anonymous Functions and Arrow Functions

Anonymous functions and arrow functions provide concise ways to define functions:

const square = function(x) {
return x * x;
const double = x => x * 2;

Callback Functions

Callback functions are functions that are passed as arguments to other functions and are executed later:

function process(callback) {
process(function() {
console.log("Process complete!");


JavaScript functions are powerful tools for encapsulating and reusing code. By understanding how to define, call, and use functions effectively, you can write more organized and maintainable code in your web applications.

Happy coding!