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Introduction to JavaScript: Execution, Usage, and Environments

Table of Contents

    Introduction

    JavaScript (JS) is a high-level, dynamically typed and traditionally interpreted programming language primarily used for web development.

    Why use JavaScript?

    • JavaScript enhances the user experience by enabling dynamic and interactive web pages. It allows you to manipulate webpage content, add functionalities, animations, and more.
    • JavaScript supports both client-side and server-side development.
    • It is also used in full-stack development, mobile apps (React Native), and game development.

    How is JavaScript used?

    • Client-side : Embedded in HTML using <script> tag. Executed within a web browser.
    • Server-side : Used with javascript runtimes (like Node.js) for backed development.
    • Embedded in Applications : Many applications embed JavaScript engines (e.g., Electron, Tauri, React Native) to enable cross-platform development. Some game engines, like Unity, also support JavaScript.

    How is JavaScript executed?

    "JavaScript runs differently depending on the environment. Below are some widely used execution methods:

    In browser

    • Loading : Browser loads the javascript code from server. (you can write on console also)
    • Execution : Browsers have inbuilt javascript engines (an isolated environment for js execution), these engines are used to run loaded javascript code.
      • Javascript engines : These engines only understand JavaScript (ECMAScript standard). They rely on external APIs (provided by browsers or runtimes) to interact with the outside world.
    • A browser environment have JS engine(V8), Web APIs(DOM ...), Event Loop & Callback Queue

    In runtimes (Node.js,deno ...)

    • Coding : Javascript code is written in a file, with .js extention.
    • Execution : A javascript engine within the runtime is used to run the javascript code.
    • A runtime have JS engine(V8), Event loops(asynchronous tasks ...), APIs and system access(file handling ...), External libraries(npm ...) which makes it more flexible.

    Frequently Asked Questions

    What is JavaScript?➕

    JavaScript (JS) is a high-level, dynamically typed, interpreted programming language primarily used for web development.

    Why is JavaScript used?➕

    JavaScript enhances user experience by enabling dynamic and interactive web pages. It supports both client-side and server-side development and is also used in full-stack development, mobile apps, and game development.

    How is JavaScript used in client-side development?➕

    JavaScript is embedded in HTML using the <script> tag and executed within a web browser to manipulate content, add functionalities, and enhance interactivity.

    How is JavaScript used in server-side development?➕

    JavaScript is used with runtime environments like Node.js to build backend applications, allowing server-side scripting and database interactions.

    How is JavaScript embedded in applications?➕

    Some applications embed JavaScript engines, such as Electron for desktop apps, Tauri for lightweight applications, and React Native for mobile development.

    How does JavaScript execute in a browser?➕

    The browser loads JavaScript from the server and runs it using its built-in JavaScript engine (like V8). The browser environment includes a JS engine, Web APIs, an Event Loop, and a Callback Queue.

    What are JavaScript engines?➕

    JavaScript engines, such as V8 (Chrome, Node.js), SpiderMonkey (Firefox), and JavaScriptCore (Safari), interpret and execute JavaScript code following the ECMAScript standard.

    How does JavaScript execute in runtimes like Node.js?➕

    JavaScript code is written in .js files and executed using a JavaScript engine (e.g., V8 in Node.js). Runtimes provide additional APIs for file handling, networking, and asynchronous tasks.