JavaScript is a versatile programming language that brings websites to life. Unlike static HTML and CSS, JavaScript adds interactivity, allowing users to click buttons, fill forms, and see dynamic content updates without refreshing the page.
Client-side JavaScript runs directly in the user's web browser. When you click a button or type in a form, JavaScript immediately responds without needing to contact the server. The JavaScript engine processes your code, manipulates the DOM to update the page content, and handles user events in real-time.
Server-side JavaScript runs on servers using Node.js runtime environment. Unlike client-side JavaScript that runs in browsers, server-side JavaScript can access databases, file systems, and handle backend operations. When a client sends an HTTP request, Node.js processes it, interacts with databases or files, and sends back an HTTP response.
This JavaScript code example shows how to create interactivity. We define a function called greetUser that displays an alert message. Then we use addEventListener to attach this function to a button's click event. When the user clicks the button, JavaScript executes the greetUser function and shows the Hello World alert.
JavaScript has evolved into a versatile language powering diverse applications. It creates interactive web applications using frameworks like React, builds mobile apps with React Native, handles server-side operations through Node.js, and even develops desktop applications using Electron. This versatility makes JavaScript one of the most important programming languages in modern software development.