Introduction to JavaScript

You are reading Part 1 of the 39-part series: JavaScript Skill Progression: The Path from Beginner to Extreme. [Level 1]

What is JavaScript?

JavaScript is a high-level, interpreted programming language that enables dynamic behavior on web pages. It was created by Brendan Eich in 1995 and has since become one of the core technologies of the web, alongside HTML and CSS. JavaScript allows developers to create interactive and engaging web experiences by manipulating the Document Object Model (DOM), handling user events, and dynamically updating content without requiring a page refresh.

JavaScript follows the ECMAScript standard, which ensures consistency across different environments. The language has evolved significantly over the years, introducing new features like arrow functions, async/await, and ES6 modules, making it more powerful and developer friendly.

JavaScript is a versatile and powerful programming language that plays a crucial role in modern web development. Whether it’s creating interactive websites, building backend services, or developing cross-platform applications, JavaScript remains an essential skill for developers. Understanding how it works and where it runs is the first step in mastering the language and unlocking its full potential.

How JavaScript Works

JavaScript is a single-threaded, event-driven language that executes code in a sequence known as the Execution Context. It uses the JavaScript Engine, which interprets and executes the code. The engine consists of three main components:

1. Memory Heap – Stores variables and objects.

2. Call Stack – Keeps track of function execution.

3. Event Loop & Callback Queue – Manages asynchronous operations, ensuring smooth execution of tasks like API requests and UI interactions.

JavaScript code runs inside an execution context, starting with the Global Execution Context, followed by individual Function Execution Contexts as needed. This allows JavaScript to manage scopes and closures efficiently.

Where JavaScript Runs

JavaScript can run in various environments, including browsers and server-side platforms:

1. In Web Browsers

JavaScript is primarily known for running in web browsers. Every modern browser, such as Chrome, Firefox, Safari, and Edge, has its own JavaScript engine:

• V8 (Google Chrome, Edge)

• SpiderMonkey (Mozilla Firefox)

• JavaScriptCore (Nitro) (Apple Safari)

These engines compile JavaScript into machine code, optimizing execution speed. JavaScript in the browser allows for:

• DOM manipulation to update web page content dynamically.

• Handling user interactions (clicks, keyboard input, etc.).

• Making HTTP requests (AJAX, Fetch API) for data retrieval.

• Running animations and visual effects.

2. On the Server (Node.js)

Node.js is a runtime environment that allows JavaScript to run outside the browser, enabling backend development. It is built on the V8 engine and provides additional capabilities, including:

• File system access (reading/writing files).

• Running web servers (using frameworks like Express.js).

• Database interaction (MongoDB, PostgreSQL, etc.).

• Handling concurrent network requests efficiently with an event-driven, non-blocking I/O model.

3. Other Environments

JavaScript is also used in:

• Desktop Applications (Electron.js for cross-platform apps like VS Code and Slack).

• Mobile Applications (React Native for iOS and Android development).

• Internet of Things (IoT) (Running on microcontrollers and smart devices).

• Game Development (Using libraries like Phaser.js and Three.js for 2D/3D games).

You are reading Part 1 of the 39-part series: JavaScript Skill Progression: The Path from Beginner to Extreme. [Level 1]