A high-level, often just-in-time-compiled language that conforms to the ECMAScript standard, JavaScript (JS) is a core technology of the Web alongside HTML and CSS. Created by Brendan Eich in 1995, it is maintained by Ecma International’s TC39 technical committee. As of 2025, JavaScript is the most widely used programming language on GitHub, though TypeScript, a statically typed version of JavaScript, overtook it by August 2025.
Client-Side Scripting and Execution
JavaScript is primarily used for client-side scripting, running directly in web browsers. This allows websites to respond to user actions in real time without reloading the entire page. Web browsers have dedicated JavaScript engines that execute the client code, and these engines are also utilized in some servers and a variety of apps. The most popular runtime system for non-browser usage is Node.js.
Cross-Browser Compatibility
JavaScript is supported by all major web browsers, making it a reliable choice for web development. Developers can write code that works consistently across different browsers, ensuring a uniform user experience.
Interactivity and Dynamic Functionality
JavaScript creates interactive website features, such as form validation, image sliders, and pop-up windows. It enables user engagement and a smoother user experience by allowing dynamic manipulation of the Document Object Model (DOM), which represents the structure of a web page.
Frameworks and Libraries
JavaScript has a rich ecosystem of frameworks and libraries, such as jQuery, React, and Angular. These tools simplify and accelerate web development by providing pre-built functions and components.
AJAX and JSON
JavaScript, along with technologies like XML (Extensible Markup Language) and JSON (JavaScript Object Notation), enables asynchronous communication with web servers. This technique, known as AJAX (Asynchronous JavaScript and XML), allows web pages to update content without full page reloads, enhancing user experience. JSON is a lightweight, human-readable data format often used with JavaScript to exchange data between a server and a web application.
