Node.js, Browser & Global Objects

1. JavaScript Engines

• A JavaScript engine is the program that executes JavaScript code.

• Different environments use different engines:

  • V8 Engine (by Google) → Chrome, Edge, Opera, Brave, Node.js.

  • Spider Monkey (by Mozilla) → Firefox.

  • JavaScriptCore (by Apple) → Safari.

• Engines parse, compile, and run JavaScript.

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2. Node.js Environment (Server-Side JavaScript)

⚡ V8 Engine in Node.js

• V8 engine is embedded inside Node.js.

• Without Node.js, the V8 engine alone cannot run system-level tasks (like file handling, networking).

• Node.js provides the bridge between raw JavaScript execution (V8) and operating system capabilities.

⚡ Special Powers of Node.js

Node.js gives JavaScript additional global objects that are not part of plain JS or browser environment:

• setTimeout(callback, ms) → Run a function after a delay.

• setInterval(callback, ms) → Run a function repeatedly after intervals.

• clearTimeout(id) → Cancel a setTimeout.

• clearInterval(id) → Cancel a setInterval.

• Microservices & MicroProcess → Handle asynchronous tasks, background jobs, and OS-level processes.

➡️ These features are available via Node.js Global Object.

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3. Browser Environment (Client-Side JavaScript)

⚡ Global Object → window

• In browsers, the global object is called window.

• Running console.log(this) at global scope → refers to window.

• The window object provides access to:

  • alert() → Popup messages.

  • document → Access and modify the DOM.

  • setTimeout / clearTimeout → Timers.

  • setInterval / clearInterval → Repeated timers.

➡️ Browsers automatically provide these APIs because they are needed for interacting with the webpage.

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4. Unifying the Global Object

⚡ Problem Before ES2020

• In Browser → global object = window.

• In Node.js → global object = global.

• This difference confused developers.

⚡ ES2020 Solution → globalThis

• Introduced in ES2020.

• A universal way to access the global object across environments:

  • In Browser → globalThis === window.

  • In Node.js → globalThis === global.

• Example:

    console.log(globalThis);
  

  Works the same in both Node.js and Browsers.

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5. Key Differences: Browser vs Node.js

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6. Key Takeaways

1. Node.js = V8 + Special Powers
   (system-level features like file system, networking, microservices).

2. Browser = JS Engine + Window Object
   (DOM, UI events, alert, document, timers).

3. globalThis (ES2020) solved the inconsistency of global object references.

4. Engine dependency:

   • Chrome/Edge/Opera/Brave → V8.

   • Firefox → Spider Monkey.

   • Safari → JavaScriptCore.

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🔥 So, in simple words:

• Browser: makes JS interact with the webpage.

• Node.js: makes JS interact with the operating system.

• globalThis : make your code work consistently in both.