3.1. Javascript

3.1.1. Introduction

JavaScript is a powerful and versatile programming language developed in the mid-1990s to enhance web pages by allowing them to respond to user interactions. Unlike HTML, which primarily defines the structure of a web page, JavaScript allows developers to make web pages dynamic. This means that a website can change and respond to what you do—like when a button click updates part of the page without needing to reload the entire site.

Initially designed to run inside web browsers, JavaScript quickly gained popularity because of its ability to bring websites to life. With JavaScript, developers could create interactive features like animations, form validations, and real-time content updates. By the early 2000s, JavaScript had matured into a commercially viable tool, allowing web pages to include complex programs that could execute directly in the browser. This meant that websites could provide richer experiences, ranging from simple interactions to fully-fledged applications.

Today, nearly all websites use JavaScript in some way, and many are entirely dependent on it. For example, popular services like social media platforms, streaming sites, and online games all rely on JavaScript to function. The language’s growth has been so significant that even computer hardware manufacturers now design their processors to optimize JavaScript performance, ensuring websites run smoothly on all kinds of devices.

JavaScript is essential for modern web development. Its ability to handle everything from basic user interactions to complex applications has proven invaluable.

3.1.2. Javascript Browser Model

When you visit a website, your browser downloads and processes (or “parses”) the HTML, CSS, and JavaScript files that make up the page. HTML structures the content, CSS styles it, and JavaScript adds interactivity. JavaScript can be embedded directly within an HTML file using <script> tags, known as inline scripts, or it can be served in a separate file, linked in the HTML through a <script> tag, known as an external script.

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As the browser parses the HTML, it encounters these script tags and executes the JavaScript code. Inline scripts are run immediately as the browser reads them, while external scripts are fetched from their source and then executed. JavaScript can manipulate the content on the page, respond to user interactions, or fetch additional data from the internet, making web pages dynamic and interactive.